Bitcoin-Qt wallet shows outgoing transaction as "Offline (0 confirmations)" What is the meaning of a transaction status of "Offline (0 confirmations)" as opposed to "Unconfirmed (0 confirmations)" ?

Does it mean that the transaction has not even been sent to the network yet?
If so, why would that happen, and can I force it to retry?

The wallet is online (13 active connections to the network), but out-of-sync (catching up very slowly, last received block was 1100 days ago).
Offline means that the transaction hasn't been sent to the network, that is, it's not in the memory pool of any other node.

Unconfirmed means that the transaction has been sent to the network and exists in the memory pools of many other nodes.

If the wallet is out-of-sync, that would be the reason it's got 0 confirmations. Even if you did have a confirmation, your node wouldn't know it since the transaction would be in one of the newest blocks.

If the transaction is not on blockchain.info, there's a very good chance that it hasn't been sent. You should probably resend it using the instructions found here.