Meta coins are just another name for altcoins that are issued on the ledger of another coin or cryptocurrency platform.

IE Ripple, Mastercoin, Ethereum, NXT are example of standalone blockchains/legers where you can issue new coins that transact on top of that network.

metacoins can also be referred to as Digital Assets, Smart Contracts, DACs, DAOs, etc. There's a lot of buzz words around altcoins, the terms are fragmented since the industry is just starting.