Oh Happy Day kommt aus dem Englischen und bedeutet frei übersetzt so viel wie:"was für ein schöner Tag", wenngleich es wörlich übestezt:"oh du glücklicher Tag" bedeutet.
Bekannt wurde dieser Ausruf vor allem durch ein Lied welches auf dem Soundtrack zu finden ist und im gleichnamigen Film von einigen Nonnen gesungen wird ( unter anderem auch Whoopy Goldberg ).
Anbei habe ich den Songtext mit angefügt

Oh happy day (oh happy day)
Oh happy day (oh happy day)
When Jesus washed (when Jesus washed)
When Jesus washed (when Jesus washed)
When my Jesus washed (when Jesus washed)
He washed my sins away

He taught me how (oh, He taught me how)
To wash (to wash, to wash)
Fight and pray (to fight and pray)
Fight and pray
And he taught me how to live rejoicing
yes, He did (and live rejoicing)
Oh yeah, every, every day (every, every day)
(oh yeah) Every day!

Oh happy day (oh happy day)
Oh happy day, yeah (oh happy day)
When Jesus washed (when Jesus washed)
When my Jesus washed (when Jesus washed)
When Jesus washed [hits high note] (when Jesus washed)
My sins away (oh happy day)
I'm talking about that happy day (oh happy day)

He taught me how (oh yeah, how)
To wash (to wash)
Fight and pray (sing it, sing it, c'mon and sing it)
Fight and pray
And to live
yeah, yeah, c'mon everybody (and live rejoicing every, every day)
Sing it like you mean it, oh....

Oh happy day (oh happy day)
I'm talking about the happy days (oh happy day)
C'mon and talk about the happy days (oh happy day)
Oh, oh, oh happy days (oh happy day)
Ooh talking about happy day (oh happy day)
Oh yeah, I know I'm talking about happy days (oh happy day)
Oh yeah, sing it, sing it, sing it, yeah, yeah (oh happy day)
Oh, oh, oh
Oh happy day.....