about to

About + infinitive (with to) means ‘going to very soon’; ‘just going to’.
Don’t go out now – we’re about to have lunch.
I was about to go to bed when the telephone rang.
Not about to
can mean ‘unwilling to’.
I’m not about to pay 100 dollars for that dress.
about to
• see adverb position 5: emphasizing adverbs

For more information consult a good dictionary like Langman, Oxford, Merriam Webster, or Collins.