As a newbie to the field of toy collecting in general, it can be somewhat daunting. You can also be taken for granted if you are not careful... here are some common acronyms and terms to help jumpstart you.

General Action Figure Collecting Acronyms and Terms

c1-c10. Basically, c10 means that the toy is perfect and c1 means it's good for target practice. It's very much opinion-based. You will very rarely see any item for sale below c6 quality. Anything above a c8 is good to buy, but always try to get a picture before the deal.

Loose. Contrary to popular belief among newbies to the field (and occasionally even some veterans), loose does not mean that the toy is out of its original packaging AND has no accessories. Loose simply means that the toy is out of its original packaging. It is usually implied that these are complete unless otherwise noted.
Complete. Toy comes with all accessories.

Incomplete. Toy comes with some accessories.

Bare. Toy comes with no accessories.

MOC. "Mint on Card." This means that the action figure is unopened. If you see c1-c10 before MOC, it means the actual card (the cardboard backing) is in that condition, not the figure.

Punched. Hole near the top of the card has been punched to allow the figure to hang on the pegs in the store.

Unpunched. Hole has not been punched.

MISB. "Mint in Sealed Box." Box has never been opened, and is like it was if it was just purchased from a store. Same c10 rules apply as MOC.

MIB. "Mint in Box." This implies MISB usually, but it should be noted if it has been opened. Inquire if you are unsure. Same c10 rules apply as MOC.

MISP. An all-encompassing acronym that means "Mint in Sealed Package." Same c10 rules apply as MOC.

MIP. An all-encompassing acronym that means "Mint in Package" if applied to a box, or alternatively "Mint in Plastic" if applied to a carded figure. This usually implies MISP, but it should be noted if it has been opened. Inquire if you are unsure. Same c10 rules apply as MOC.

FS. "For Sale."

FT. "For Trade."

FA. "For Auction."

WTB. "Want to Buy."

WTT. "Want to Trade." Can also be WTTF, meaning "Want to Trade for ..."

Masters of the Universe-Specific Acronyms

LL. "Laser-Light," as in the seventh-series European-only laser-series figures. This term is used collectively although the figures are actually called "Laser Power He-Man" and "Laser-Light Skeletor."

POG. "Powers of Grayskull," or the sixth-series Grayskull Dinosaurs (Tyrantisaurus Rex, Bionatops, and Turbodactyl). Also refers to the ultimately unproduced seventh-series "He-Ro and the Powers of Grayskull" toyline.

MOTU. "Masters of the Universe," or the original cartoon series, "He-Man and the Masters of the Universe."

POP. "Princess of Power," or the second cartoon series, "She-Ra: Princess of Power."

NA. "New Adventures," or the short-lived third cartoon series, "The New Adventures of He-Man" that ran in conjunction with the equally short-lived toyline simply called, "He-Man.