What is the word for "attend a party or event without being invited"? I read it some time back but can not recollect it.
Gatecrashing is the most common term I've heard:
To attend a social event without having been invited, or without having paid.
Are you looking for a word to describe the person who is attending uninvited, or are you looking for a word to describe the act of attending a party uninvited?
One who attends a party uninvited could be committing a "faux pas", which means a "violation of social norms or etiquette."
But the words that can be used for describing a person who commits these types of social blunders are plentiful... depending on how harsh or kind you are looking to be in portraying the person's wrongdoing.
To tag-along to a party uninvited might work. Crash the party also works beautifully.