an ancient expression of relief or excitement which has been used in many scenarios particularly in friend or social groups where a idea or issue is shared throughout it.
and the term can also be used in basketball when a person scores a particular type of shot.
for e.g. one guy says to another on a school day:
that examination was a "BIG oof"
other guy: yeah i'm finally glad its over. Oof
basketball reference:
*guy does alley oop and scores*
crowd: OOF