What does the _ (underscore) mean in a math problem?

Question

For example Z_p or Z_2?

Answer 1

It's a notation specific to writing math on the internet, and means that the character that follows is a subscript. For instance, Z_2 = Z₂. The notation exists because in most cases there's no simple way to display the character as an actual subscript (the particular case I just showed is an exception, but it won't show up on everyone's browser, since not all browsers correctly implement the unicode subscript characters.

As for what Z_p itself could stand for, in group theory it stands for the ring of integers mod p.

Answer 2

Hi,

The underscore in a maths problem means "sub(scripted with)".
Ex: "x_2" means "x subscripted with 2". Often used to express sequences with index.

Hope it is useful :-)