Basic lunges are usually performed with an upright torso, but they can be done with your torso bent slightly forward at a 45-degree angle. That way, at the bottom of each rep, the dumbbells end up on each side of your front foot instead of by your hips.
An upright torso places more emphasis on the quads while a forward trunk lean can increase the recruitment of the glutes and hamstrings. And the torso angle can be tweaked. The more forward the torso is leaned, the more demand you place on the glutes and hamstrings, which reduces the demand on the quads.
The 45-degree forward lean provides a nice middle-ground torso position that places more demand onto the glutes and hams than the conventional style (with an upright torso) while still placing an overload demand on the quads.