The use of multiple accounts in one universe by a single user. Each user is limited to one account per universe, thus those who are caught are punished by permanent bans in that universe. Per Game Operator's (GO) discretion, the smallest account may be released from ban. However stronger players take advantage of the multi-account rule & the naive GOs forcing strategic hits to the enemy. So next time you see someone in your Universe doing better than average be sure he has a bogus second/third or even fourth account he is using to farm or even create or join a bogus alliance.
A new term most often related to Multi Accounting would be to "SoG". When someone is Sogging, they are drenching the universe in accounts that are unnecessary.