(back) in the day

[Jonathon Green]

'Back in the day' (which on the whole seems to exist of itself without any
continuing 'when...') seems to mix the meanings of 'once upon a time', 'way
back when' and the '(good) old days'. The phrase seems to have been
popularised (and coined?) by the hip-hop/rap community and emerges around
the early 1990s, when the reference is often to what is known in rap as 'old
school', i.e. the early East Coast hip-hop pioneers of c.1975-1980 such as
DJ Kool Herc, Afrika Bambataa or Grandmaster Flash. This would mean that the
initial amount of time passed was around a decade, but I don't think this is
mandatory. In this context at least, cultural 'back-ness' (as it were) is as
pertinent as temporal.

Jonathon Green