To give the impression of having more than what you have.
To pretend to be someone you are not.
To flaunt material possessions that are not rightfully yours.
To buy more than what you can honestly afford.
Or in the words of Word Reference, (Méx) (=impresionar) to impress; (=achatar) to crush, overwhelm; (=dejar boquiabierto) or to fill with wonder.
Take your pick of the definition. Whatever the case, it’s one of those words that’s hard to resist using once you know what it means.
What other Spanish words do you like to use?