lastlog is an old ircII terminus standing for log of last messages. It was coined by BigCheese, original author of ircII.
psyced implements this concept on the server side rather than on the client side. It is used to keep messages stored for you, and generally to let you have your last session's backlog back when you log in.
- _match: a substring contained in the log
- _amount: the number of messages to roll back
- _parameter: you don't know what the user typed - could be a match or an amount or something new we don't yet know about.