Hexagon - A six sided and six angled polygon. Hex means 6.
Histogram - A graph that uses bars where each bar equals a range of values.
Hyperbola - One type of conic section. The hyperbola is the set of all points in a plane. The difference of whose distance from two fixed points in the plane is the positive constant.
Hypotenuse - The longest side of a right angled triangle. Always the side that's opposite of the right angle.