Exposure latitude is the range of acceptable exposure values for a given film.
To say that a film has a lot of exposure latitude means that there is a large difference between the amount of light that makes it go completely black and the smallest amount of light that manages to make an impression on it.
Exposure latitude is normally measure in f-stops.
A film with a lot of exposure latitude is perceived as "forgiving": your exposure can be off one or two stops, and the negative is still printable.
Negative prints generally have much more exposure latitude than slide films. Some contrasty slide films, like Velvia are especially bitchy: with these films, a half stop error is visible.