Quad is short for quadrilateral, a 4 sided shape. Quad meshes are ideal for digital sculpting and 3d animation. Sculpting on a mesh with a mixture of quads and non quads can result in pinching and sharp angles in unwanted areas. Here I present some cases where polygons can be converted into quads.
1) Quad adjacent to a triangle
Add a line in the centre of the quad.
2) Two Quads adjacent to a pentagon (5 sided polygon)
Add a line to the centre of the pentagon.
3) septagon (7 sided polygon) sandwiched between 4 quads and 2 quads
Split the septagon as shown.
4) Ring of triangles (even number)
Remove half the lines to merge triangles into quads.
5) Ring of Triangles (odd number)
Remove half the lines and add a point to the remaining triangle.