Alternate spelling of "oof", which is an onomatopoeia (word that sounds like the noise it describes or refers to, in this case the sound a
person makes upon impact with an unexpected force that knocks the breathe out of them).
It is more of a 'sound effect' than an actual
word, used to indicate that someone feels the impact of a powerful or meaningful statement someone made, or sympathizes with the crushing blow another
person experienced. In this regard, it's a synonym for "ouch".
This alternate spelling
may be used as a stylistic preference, or to avoid the confusion of this now somewhat uncommonly used
word being mistaken as a typo of "of" or "off".