A transaction byte-encoded using the Recursive-Length Prefix (RLP) algorithm. Before Constantinople, it needs to be signed before it will be accepted by the network.
A raw transaction is a transaction encoded using the RLP algorithm.
Before Constantinople, it needs to be signed.
The result is a sequence of bytes that is ready to be posted to the Ethereum network.
See https://github.com/ethereum/EIPs/pull/208 for changes planned for Constantinople.