A 12-sided two-dimensional polygon is called a dodecagon. A regular dodecagon has 12 sides that are all the exact same length and internal angles that are 150 degrees each. Since there are 12 internal angles, the total internal angles add up to 1,800 degrees.
A polygon refers to any two-dimensional shape that consists of only straight edges and has a closed shape. The most common polygons are those with a small amount of sides, such as triangles with three sides and squares with four sides. A dodecagon has 12 straight edges in a closed loop along with 12 vertices where the edges meet.