If the bottle is from France, a Chablis is made of 100% chardonnay grapes grown from the Chablis region. If the bottle is from the USA, a Chardonnay must have at least 80% chardonnay grapes grown from anywhere. If the bottle says Chablis and is from the US, all bets are off. It could have nearly anything inside. Many US bottlers in the 1970's started using the term "Chablis" to mean "white wine."
It's a white wine, usually a chardonnay. ------------------------ Any wine bearing Chablis on the label will be a white wine made 100% from Chardonnay. Other grape varieties are made into wine in the general area of Chablis, however they are not permitted to use Chablis on the label (they have to use the generic Bourgogne AOC designation instead).
A chardonnay would go nicely with foie gras. It's a bit sweeter and has a rich buttery kind of taste to it. However, a French unoaked Chardonnay, for example a white Burgundy, would be too dry and minerally. The ultimate pairing for foie gras is a good Sauternes, which is sweet, but has a unique flavour due to the "noble rot" on the grapes. Make sure it's chilled!