UniteKeyCreator \ Modify \ Boolean \ Unite
Use this option to collect bodies into one body. The bodies do not have to intersect. Disjoint bodies will not be relocated to intersect. Instead, they will remain disjoint in the single body. (The Combine Disjoint Bodies function is a faster way of uniting disjoint bodies.) You can select solids in part references as tool solids. In all such cases, the tool solid (which is a solid in a part reference) is never destroyed.
NOTE: The united body is recognized as a single entity. See also Trim/Split a Solid to Another Solid.
Using the Function: