noun
The definition of a gate crasher is a person who attends some event or social affair without being invited or without having proper credentials (like a ticket) to get in.
An example of a gate crasher is a person who just shows up and comes into a party uninvited.
gate-crasher

Informal a person who attends a social affair without an invitation or attends a performance, etc. without paying admission
gate-crasher

Noun
(plural gatecrashers)
- (slang) A person who enters some event without a ticket or invitation, either by sneaking in, or talking their way past a ticket taker, or some other stealthy technique, rather than a confrontational encounter.
Origin
gate crash + -er