What is the meaning of the word "ad hoc"?

Definitions:

  1. for one specific case copy to clipboard adverb
    • they were appointed ad hoc copy to clipboard
  2. for or concerned with one specific purpose copy to clipboard adjective
    • a coordinated policy instead of ad hoc decisions copy to clipboard
  3. often improvised or impromptu copy to clipboard adjective
    • an ad hoc committee meeting copy to clipboard