A pressie is a present — a gift. It is friendly, spoken English, mostly British and Australian. You unwrap a pressie at a birthday; you do not put it in a formal letter. Friends say it to friends, and adults say it to children. A boss would not write it in an email about a company gift. The spellings pressie and prezzie both appear. Though actually, it is just present with a warm little ending, the same kind of ending as in movie or auntie, so it feels small and kind even when the gift is not small.