Default UI Menu: Modify/Modify 3D Objects/Surface Mesh/Join Coplaner Faces
Ribbon UI Menu:
Combines selected faces which share a common plane into a single face.
To Combine faces:
Select the tool.
- Click finish.
Use Neighbor Faces: When this option is on the resulting face will be formed from all faces on the object which are co-planar, and connected on that plane to the selected faces.