One way to hold this word: it names a group and a sexual act, and it says nothing at all about whether the people involved agreed. That silence is the whole problem with it. One meaning describes something everyone chose; the other names a crime. Because the same crude slang covers both, a listener often cannot tell which is meant — which is exactly why careful speakers reach for the plain terms, 'group sex' and 'gang rape', and why this word is one to recognise rather than to use.