A seven-sided shape is called a heptagon. Some people refer to heptagons as septagons, but this mixes a Greek suffix with a Latin prefix, so it is not the preferred usage.
A heptagon is a type of polygon, which Math.com defines as a plane figure with several line segments that join together but do not intersect. All of the angles and sides are equal in a regular heptagon.
In Germany, the Mausoleum of Prince Ernst was constructed using a heptagonal floor plan. This type of floor plan is rarely used in architecture. The Barbados dollar coin is also in the shape of a heptagon.