A tessellation is a series of interlocking shapes that fit together without gaps or overlaps. Common examples of tessellations include bathroom tiles, subway tiles, puzzles, checkerboards, chessboards, Chinese checkers boards, and honeycombs. The document then provides instructions for creating a hexagonal tessellation out of triangles by drawing symmetrical faces, cutting out triangles, tracing halves of faces on the edges, flipping and tracing the backs, cutting out more triangles, and gluing them together to form a hexagon.