While statement without expression

Here is a part of a code in Python I try to figure out what it is doing:

while index < len(list) and list[index]: index += 1

I wonder what the part after the "and" (and list[index]) does exactly? I tried to add "is True" or "is False" but both did not yield the same result, so it does not check for True or False I guess. Thanks for any help!