the '70s; the seventies
Refers to the decade from 1970 to 1979. Often used in historical, cultural, or fashion contexts.
７０年代の音楽が好きです。
I like music from the '70s.
この建物は７０年代に建てられました。
This building was built in the seventies.
Common ASCII variant; same reading and meaning.
Compound of ７０ (ななじゅう, 'seventy') and 年代 (ねんだい, 'era, decade').