a type of punk rock featuring violent, racist lyrics, associated esp. with skinheads.
oi or oy: —interjection
used to express surprise, pain, grief, worry, etc.
oi (World English Dictionary):
1. (Brit ) a cry used to attract attention, esp in an aggressive way
2. of or relating to a form of punk rock popular esp among skinheads in the late 1970s and 1980s.
Word Origin & History:
oi: 1962, vulgar or working class pronunciation of hoy a call or shout to attract attention.
oy: Yiddish exclamation of dismay, 1892, Amer.Eng. Extended form oy vey (1959) includes Yiddish vey , from Ger. Weh "woe"
Wikipedia entry for Oi!:
Oi! is a working class street-level subgenre of punk rock that originated in the United Kingdom in the late 1970s. The music and associated subculture had the goal of bringing together punks, skinheads and other non-aligned working class youths (sometimes called herberts).
So in that song, it must have been used as a music subgenre.