Because the initial position is symmetrical there are only three distinct first moves: a3-b4, c3-b4, and c3-d4.
In Brettspiele der Völker, Lasker gives names to several openings:
The Hague opening
Black can continue with g5-f4 or c5-b5.
The Berlin defence
Black can also play d6-e5.
The Wing gambit