What's the difference between push-ups and press-ups? I browsed the Internet but it seems that both words are used interchangeably.
They are one and the same thing, although "press-up" is British whereas "push-up" is American.
The online Oxford dictionary says of "push-up": Another term for press-up. Chiefly North American
And of "press-up": An exercise in which a person lies facing the floor and, keeping their back straight, raises their body by pressing down on their hands:
@nxx's answer is interesting about using "press-up" in Oz. I always assumed that "push-up" was the British usage, since that's what we say here in South Africa, and we used to be a British colony.