I am having trouble understanding what a cosmic inflation is.

Please try to suffice an explanation for non physicists / non formal students for physics / general audience.

I understand that an inflation situation usually means a process where something is growing in volume but not in mass ; like inflating a balloon or making prices higher in general although the money worths pretty much the same in worldly currency trade.

Given that our universe expands (an expansion which isn't considered "inflation" for some reason) in a void which might include one or more other universe/s (static or expanding), what could be an "inflation" in that regard?

The only thing I could imagine is when quantum particles "suddenly" appear in another area in the void to form a new universe or to expand an existing universe.