Edit > Group

Groups objects together under a new transform node, allowing you to select and transform them all at once.

Edit > Group >

Group Under

Group objects under one of the following:

Parent: Groups the selected objects under their lowest common parent in the hierarchy. For example, selecting a single object and grouping puts the group node immediately above the selected object in the hierarchy.

Selecting objects that are in different hierarchies puts the group under the world since they don’t share a common parent.

Selecting objects in different parts of the same hierarchy puts the objects under their lowest common parent. If you go from each selected object, the new group will be placed under the first node containing all the selected objects.
World: Puts the new group under the world (at the top level of the hierarchy).

Group Pivot

Select where you want the pivot point for the group to be.

Center: Puts the new group’s pivot point at the center of the bounding box of the grouped objects.
Origin: Puts the new group’s pivot point at the origin of the new group’s coordinate system.

Preserve Position: Turn this option on to modify the selected object’s matrix so that Maya preserves the overall world-space position of the object. If turned off, the matrix of grouped objects are changed and the object’s world-space position changes when grouped.