This is an ongoing thing, so bear with me. Please contribute anything you don't see here.
3x1 vs. 2x1 weave
This refers to the number of weft threads per warp thread. Most denims have been traditionally 3x1 weaves, though lighter weight denims (under 10.5 ounces/sqare yard) often use the 2x1 configuration. [from LA Guy]
The quick definition can be summed up in one word, "horrible". Also called "Snow wash". This technique reared it head up in Italy in the late 80s. Basically you soak your pumice stones in bleach and tumble them with the jeans. Then neutralise. [from ringring]
"Big E" jeans refer to Levi's jeans produced before 1971, in which the red tab on the back pocket had the LEVI'S logo with a capital E. Post-1971 Levi's jeans are written "LeVI'S" on the red tab.
Instead of the twill running to the right or left, broken twill jeans (traditionally considered the cowboy-preferred denim) contain no distinct direction of weave. The weave is instead alternated right and left - the end effect resembles a random zig-zag. Wrangler made the first broken twill jeans in 1964. Broken Twill was designed to combat the twisting effect that was a characteristic regular twill (and considered a 'fault' by many at the time). By going on both directions, the tension in the yarns is balanced in Broken Twill. [additions from ringring]
Also called RingxRing, Ring-Ring, Double Ringspun. Dual ring-spun denim is denim where both the warp and weft (filler) threads are made of ring-spun yarn. Typically only premium, more expensive denim brands use this method, as it is more labor intensive and thus more costly to produce. The result however, is a very textured denim, and is much softer than open-end or single ring-spun. You will know ringspun denim when you see it - the warp threads will be "slubby" at some points, and there will be little puffs of indigo thread. It is more obvious when looking at the weft threads (underside of the denim).
The environmentally friendly way to stone wash jeans, through the application of organic enzymes that eat away at the fabric, i.e. the cellulose. No pumice stones are used. When the desired colour is achieved, the enzymes can be stopped by changing the alkalinity of the bath or its temperature. A final rinsing and softening cycle is next, before the jeans are ready to be sold. Still frowned upon by companies such as Howies, who prefer to use rubberised "Eco" Balls to wash their jeans. [from Cake]
Left Hand Twill
This refers to the direction that the denim is woven. Left hand twill denim is softer to the touch than right hand twill, and was originally used by Lee denim. Now used by other denim companies such as 45rpm, Kunna, and Lee Japan. Left hand twill is easy to spot, as the weft threads appear to move upward and to the left as opposed to upward and to the right.
Mercerising for denim is used to increase lustre, by passing the denim through a bath of caustic soda. It's a process carried out after the denim is woven and vastly different to the more commen method of mercerising yarn. As it significantly increases the cost and lead times of denim production, it is a relatively rare process. (not that many consumers would notice). [from ringring]
Sanding is basically done 3 ways: Sandblasting, (see below),
Machine sanding - just like machines that you'd use to sand a wooden table, and Handsanding aka Handbrushing - just a piece of folded fine sandpaper. All three methods are used in various ways, on the flat surfaces (tables, ironing boards), on the dummy (inflatable dummies, sometimes standing, sometimes flat, sometimes 'seated') and various templates can be used to create a 3D effect. Any sanding can be enhanced with chemical whiteners. [from ringring]
Basically dyeing over the fabric or jeans to add another tone of colour. Most often used is a 'yellowy' overdye to create a 'dirty' look. Also can be applied with spraygun or paintbrush for local colouring (ie. if you wanted just 'dirty knees'). [from ringring]
Redline refers to a colored warp thread that is run through the selvage edge of denim fabric. This is not indicitive of the quality of the jeans so much as it is a signature of the maker, and a way for Cone Mills to differentiate between the denim they made for different companies. Lee denim had a green (or sometimes blue) warp thread on their selvage, and Wranger used yellow.
Right Hand Twill
This refers to the direction that the denim is woven. The opposite of Left Hand twill, this weave is much more common, as almost all jeans are woven with right hand twill. The weft (filler) threads will be visible in upward-right diagonal lines on right-hand twill jeans.
The method in which the yarn is produced; ring-spun cotton is spun on a ring instead of more modern method of open-ended spinning. The result is a softer denim, that is more imperfect than open-ended and has individual texture that is often desired by denim admirers.
The best method of dying denim, most (should be all) upscale denim manufacturers use this method. It refers to twisting the threads of yard into a rope-like shape, then dipping the rope into a bath of indigo. It is often dipped multiple times - the more bathing of the yarn, the darker the shade.
As it sounds, compressed airguns shoot sand onto jeans to create abrasion. Sometimes a 'tracer' dye is added so that the 'shooter' can more accurately judge the volume and accuracy. Very fast, but quite a clumsy way to achieve fading. [from ringring]
Sanforizing denim is a method of stretching and manipulating the cloth in the factory prior to any washing so that any shrinking during future washes will be minimalized. It is important to note if your raw jeans are sanforized or not before determining what size to buy, non-sanforized jeans will shrink 7-10%, while sanforized jeans will shrink 1-5%. It is often advised to give non-sanforized jeans a warm soak before wearing them to get the shrinking done before you create wear marks on the jeans.
Selvage (Selvedge) Denim
Selvage and selvedge mean exactly the same thing - different companies spell it differently and there apparently is no "right" way to spell it. It comes from the phrase "self-edge" which refers to the edge being finished by the loom instead of sewn together after weaving. [thanks Geowu]. Selvage is the term commonly used to refer to denim that has been produced on a shuttle loom. Since the amount of fabric produced from a shuttle loom is significantly narrower than a projectile (wide) loom, the cotton consumption is higher and the time required is greater. In selvage jeans, you will see the actual edge of the fabric where the weaving stops and is finished by the loom, as opposed to denim woven on a projectile loom, where the fabric has been cut off at the ends. The "redline" selvage is Levi's signature and was used in all their jeans up to 1982, before Cone Mills nixed them for the more modern projectile looms, which are faster and much more efficient.
French husband & wife team, Marithe & Francois Girbaud claim to have pioneered this technique of washing jeans in a machine with small pumice stones. Independently, the Japanese jeans company, Edwin also make this claim. The pumice stones are generally taken from southern Italy (the whitest and most expensive), Turkey and Indonesia (darkest and cheapest). Some claim that washing jeans with dark stones give the jeans a 'dirty' look, although this can be countered somewhat with extra rinsing in the laundry.
Also called rigid, or raw denim. Typically when denim is manufactured it is sent to a laundry to undergo many washing processes to give it a worn look. Unwashed denim, however, is not washed before it is sold to the customer (although some companies will sell a one-wash jean). It is stiff, and depending on the weight can feel as though you're walking in sheet-metal. It will also be very dark and will sometimes appear black. Traditionally, all jeans were sold unwashed and it was up to the customer to break them in.
Warp threads are the indigo-dyed thread. Also commonly called "surface threads," as they account for a majority of the thread you see on the surface. It is the opposite on the underside of the jeans, where the weft (filler) threads are more visible, and the warp threads are in the minority. They are woven in and out of the weft thread vertically to create the denim twill.
Weft (Filler) Thread
Weft, or filler, threads are traditionally ecru-colored, however many companies now bleach their weft threads or dye them. The weft is visible mostly on the underside of the denim, but resemble diagonal stripes on the surface. They are woven in and out of the warp threads horizontally to create the denim twill.
Also known as 'Cat's Whiskers'. These are the crease lines around the crotch. Industrially these can be done with laser, sandblasting, machine sanding, handsanding and abrasive rods. Same techniques are used for 'knee whiskers' (whiskers on the sides of knees) and 'honeycombs' (crease marks on the back of the knee). [from ringring]