Mesh Types
The mesh type determines the type of elements used to create mesh during automatic meshing.
Advanced
Enables you to select a Mapped Type for elements on surfaces that can be mapped to simple geometric shapes and a Free Type for elements that cannot easily be mapped to simple shapes to use when creating mesh.
Mixed

Figure 1. Mixed
Quads

Figure 2. . The sum of element densities on the perimeter of the lower surface is odd, resulting in a tria as indicated.

Figure 3. . Adjusting the bottom edge density from 11 to 10 makes the sum even and generates all-quads.
Quads Only

Figure 4. Quads Only
R-Trias

Figure 5. R-Trias
Trias

Figure 6. Trias