Base part is a master class which contains all classes related to parts, such as Part, MeshPart, WedgePart, etc.
Example: if you have to loop through a model and do smth with all parts, you check if the instance is a part. However it will not work fkr meshes if you do instance:IsA(“Part”), forcing you to check other types using or.
Instead use :IsA(“BasePart”)
Every part, meshpart etc comes under basepart.