Maya uses the groupID node to represent sets.

Most sets in Maya are composed of a single node: the objectSet node. However, component sets are different: component sets are stored within the shape data instead of the object Set node. Each shape is connected to a groupId node that stores a unique identifier (ID) in the scene for the membership of the set within a shape's list of sets.

Note: If you look at the history of a shape in the hypergraph, the groupID node is hidden by default. To view the groupID node, turn on "auxiliary nodes" display. See Show or Hide nodes.

When deforming objects, you can use a componentTag to determine what subset to deform instead of the traditional way of deforming with groupId/groupParts/objectSet nodes. See Assign Component Tags to Geometry for more information about componentTags and membership.