K-line
An IRC server's way of locking a user out entirely — and a verb for whoever it happened to.
Classic IRC servers were configured in ircd.conf, where each line began with a letter saying what it did: C and N lines for server links, I lines for who could connect, O lines for operators. A K line ("kill") barred a given user or host from connecting to that particular server. Getting "K-lined" eventually became a phrase in its own right.
A K-line applied only to the server that set it, so the banned user could often just connect elsewhere on the network. Hence G-lines and AKILLs, which propagated to every server, and Z-lines, which blocked at the IP level before anyone could even register. A channel ban is the channel operator's tool; the K-line belongs to whoever runs the server.