The term 'gatecrasher' is a noun used to describe someone who enters a place without permission or invitation. It can also refer to someone who attends a social event without an invitation. The two crossword solutions for this term are 'INTERLOPER' (10 letters) and 'INTRUDER' (8 letters). Both words refer to someone who enters a place without permission or invitation, but 'INTERLOPER' implies that the person is not welcome and is seen as an unwelcome INTRUDER. 'INTRUDER' is more general and does not necessarily imply that the person is unwelcome.