Ask the question ‘What is dolling?’ and be prepared for 20 different answers, none of which are complete.
I can tell you what I think dolling is. Dolling is a collaborative form of art for all skill levels. Dolling started out as pixel art, but has also moved into digital drawing on a smaller scale.
One artist, a basemaker, gives out a human figure in a set of poses as resource. A second artist, the doller, draws features on that base, such as hair, clothes, sometimes even the face and the shading.
Dollers who do not use bases, but still call their doll a doll, have made a ‘baseless doll’. There will be no base or base set available for other dollers. This is the contradiction for dolling being a collaborative hobby.
A doller can be both a basemaker and a doller, but not all dollers make bases. Bases and dolls are always original art, handrawn by mouse or tablet.
There are no hard limits to how big a doll can be. But generally they are small images. Sometimes they have a background, and sometimes they have a transparent background. Generally they are human or humanoid figures. As dolling is based on old dress-up games, fashion and clothing can be an important aspect of a doll.
Mostly dollers will say that a pixel doll is a pixel doll because you say so. That would be simplest.