Questions about example sentences with, and the definition and usage of "Pff"

A: it's what someone might type or write when they're frustrated, upset, or mad. it's not bff.

A: Pff is the sound someone makes as to say “yeah right”

A: It's a sound you make when you let air escape between your closed lips.

Like when you are trying not to laugh but you can't help it and let some air out.

A: It is a sound. People use it as a sound of disbelief.

A: It is not a word, it is a sound made with the mouth to express disbelief or disdain.

“Pff,” she scoffed. “You can’t be serious.”

“Did you like the movie?”
“Pff. It wasn’t the worst I’ve seen, but it was pretty bad “

A: It's kind of a dismissive sound. It means something like "Whatever.", "It doesn't matter.", or "I don't care."

It doesn't have a set meaning, but that's the general gist.

Other common "sound words" are 'ugh', 'uh', 'ah', 'oh', 'um', 'hm', 'ha', 'haha', 'psst', and 'shh'.