Lamer is a jargon or slang name originally applied in cracker and phreaker culture to someone who didn't really understand what he or she was doing. Today it is also loosely applied by IRC, BBS, and online gaming users to anyone perceived to be contemptible. In general, the term has come to describe someone who is intentionally ignorant of how things work.
The term is derived from lame. A lamer is widely understood to be the antithesis of a hacker. While a hacker strives to understand the mechanisms behind what he or she uses, even when such extended knowledge would have no practical value, a lamer only cares to learn the bare minimum necessary to operate the device in the way originally intended. Thus, a lamer is usually indistinguishable from someone who is too lame to understand why something works even if they wanted to. A lamer's attitude is summed up by the phrase, "I don't care how it works, just that it does".
This term seems to have originated in the Commodore 64 scene in the mid 1980s. It was popularized among Amiga crackers of the mid-1980s by ‘Lamer Exterminator’, the most famous and feared Amiga virus ever, which gradually corrupted non-write-protected floppy disks with bad sectors. The bad sectors, when looked at, were overwritten with repetitions of the string “LAMER!”.
Lamer is now commonly applied to individuals perceived to be contemptible. The proliferation of computer-mediated communication media such as IRC or BBSes may be partly responsible for bringing the term into common parlance.
Generally, the more specialized and developed the culture, the more lamer is used as it was defined originally. In less exclusive cultures such as online gaming and IRC, the term has lost its original meaning.
Lamer can also be synonymous with griefer in certain gamer circles, whose only reason for playing the game is to earn points (usually by killing an opponent) even if they use dirty tactics to get their way.