Acetate / Dub plate
Disc of aluminum covered with real wax (not vinyl). Manufactured in a small number for quality  testing (before the 'test pressings' on regular vinyl). Used to demonstrate how the finished vinyl record would sound. Very easily damaged, can be played only a few times. Also used greatly for DJs and Producers to create One-off records to test on the public.

b/w
backed with (b-side)

Bootleg
Illegally released record, either copying a complete record or using large parts from other record to create a new bootleg version.

Coloured Vinyl
Vinyl is actually clear in colour but a black dye is mixed in at the manufacturing process, sometimes special/limited edition pressings are made with different colour dyes.

Die-cut sleeve
Record sleeve with a big hole in the centre (so that you can read the label) usually a company sleeve.

Flexi-disc
Very thin flexible single that used to come free on magazine covers, not seen much these days

Gatefold sleeve
Sleeve for two 12"s or LPs which can be folded out or opened up 

Insert / Press Release
Printed piece of paper with additional information about the record and the artist or sometimes only with artwork. Often with promotional copies for DJs / radio stations or intended for public relation (for the press). An intact press release often increases the value of a record

LP
Long-play record = an album or a compilation

Picture Disc
Clear transparent vinyl record which has a picture of the same size welded inside the vinyl. Often with lower sound quality.

Promo / Promotional Copy / DJ Copy
Advance releases for DJ / Radio / Promotional use, usually very limited and often contain a reaction sheet.

Run Out Groove
Area on the vinyl where the track finishes playing. Usually contains etched or stamped catalogue numbers, cutting house tags and occasionally shout outs.

Shaped Disc
Special edition of a 12" picture single with a cut-out around the edge of the picture to the shape of a 7" single. Uncut test pressings are very collectable.

Test Pressing / Advance Only Pressing
After manufacturing an acetate a small number of vinyl test pressings are produced to check sound quality. They usually bear only plain white labels, sometimes handwritten labels or prints like ‘advance only’. Usually they have no catalog numbers and can be identified only by the matrix no.

White Label
Originally white labels were just test pressings, but these days many independent record labels and producers release small quantities (500-2000) of white labels for sale to test the demand before A full release.

Withdrawn
If an artist or a record company decides not to issue a certain record and orders all copies to be withdrawn and destroyed.  Some copies always survive and are very collectable.