I remember reading a story about Lawrence Revere physically eating a Five. Somehow he was able to get the card off the table and sneak it into his mouth or somehow destroy it, leaving the single-deck game with a +EV off the top!! Wonder if this is where the term comes from.
When I was starting out I thought that card eating was merely taking cards in -EV situations. These are really just the bad count indices that are mostly ignored but should be know for players who insist on sitting a grinding at tables -- which I was. Such as not doubling an 11 and taking small cards and hence "eating cards". Banging out your stiff vs the dealers stiff, again, taking cards in a bad count.
An opposite card eating approach would be in team play where one guy plays as many hands at table min and another guy plays one hand at table max. When the count goes +EV the guy playing the small multi-hands Wongs Out leaving the good count to the Gorilla. It is a good cover play that would reduce variance. Probably not to strong to use in 6 or 8 deck game. But I think this approach would soundly beat a 1 or 2 deck game with flat bets.