Noun
yoi (uncountable)
A preparatory position in karate, with the arms slightly forward, elbows slightly bent, and fists closed.
YOI (plural YOIs)
Initialism of young offender institution.
He recalls an occasion he was segregated in a YOI, held in a cell with just a metal bed frame "because in the daytime they wouldn't give you an actual mattress", he tells Radio 1 Newsbeat. Source: Internet
“There are no plans for young offenders to return to HMP YOI Grampian. Source: Internet