Use and meaning of in in an if statement

Question

In an example from Zed Shaw's Learn Python the Hard Way, one of the exercises displays the following code:

next = raw_input("> ")
if "0" in next or "1" in next:
    how_much = int(next)

I'm having a hard time understanding the meaning of in in this statement. I'm used to using if statements, such as in javascript, where the syntax is something like:

var = 5;
if (var > 3) {
    //code  to be executed
}

Is this if / in statement (in python) the same as if() in javascript?

Finding an answer to this has been tricky because the in is such a short string to narrow down an answer via search engine, and I don't know the proper name for its operation.