ircII help: bind self_insert

Usage: BIND <key> SELF_INSERT
  Causes the key it is bound to to insert itself into the input
  buffer.  This is the default binding for the alphabet keys,
  numbers, etc.  If this is bound to a meta sequence, it will
  only insert the last key hit in the meta sequence.

Note:
  This is how you "unbind" a key.