1. Close to; ready to. — Used with an infinitive.
We were about to leave when the snow began.
I haven't gone yet, but I'm about to.
Compare: GOING TO, ON THE POINT OF.
Having a wish or plan to. — Used with an infinitive in negative sentences.
Freddy wasn't about to give me any of his ice-cream cone.
"Will she come with us?" asked Bill. "She's not about to," answered Mary.
Source: A Dictionary of American Idioms