FO - Finished Object.

Frog - unraveling a project row by row.

KAL - Knit-A-Long, where a group of knitters on a forum or through a blog will all knit the same project and share their progress.

KIP - Knit In Public.

LYS - Local Yarn Shop.

LYSO - Local Yarn Shop Owner.

SABLE - Stash Accumulation Beyond Life Expectency - when your stash is so large that even if you knit/weave/crochet for the rest of your life you wouldn't be able to use it all.

SEX - Stash Enrichment eXpedition - the act of going out yarn shopping for the purpose of increasing your stash.

SnB - Stitch 'N Bitch - either referring to the books by Debbie Stoller, or referring to a local group of people who meet up to knit.

Tink - Unstitching a project one stitch at a time.

UFO - Unfinished Object.

WIP - Work In Progress.

WYIB - With Yarn In Back.

WYIF - With Yarn In Front.

YAS - Yarn Acquisition Syndrome - the inability to resist buying yarn.

YMMV - Yarn Mileage May Vary, also known as YGMV (yarn gauge may vary) and YMV (yardage may vary).