1. [1980s+] a fig. circle of information; usu. in phr. in the loop/out of the loop.
2. [1990s+] a pornographic film.
3. [2000s] (US black) sex involving several males and a single female.
4. (S.Afr. drugs) the plastic container for the heroin-derivative drug sugars n.
[1980s+] (orig. US) not in on a secret, or unaware of what’s going on.
SE in slang uses
[1940s] (Aus.) to become angry or overwrought.
wandering around; thus take it on the loop, to leave.
[1920s] (US) to capture.
[1960s+] to disturb one, to worry one considerably, to put one off one’s stride.