referring to one or more individuals or items that have already been discussed or are thought to be well-known.
or.....
used to indicate the presence of a defining or qualifying clause or phrase that follows.
Definition 1 (Verb)
Used to describe a person thinking about doing an impossibly delusional thing mostly during mealtimes or shower times, or usually when bored.
My great grandfather gets drunk a lot, and yesterday he was (1 -ing)thing at work.
Sarah was ranting about why her boyfriend, Joseph kept on being emotionally intense after an argument and just had a (1)the session.