Science, Tech, Math › Math Definition of a Base Share Flipboard Email Print Base of Triangle and Trapezoid. D.Russell Science, Tech, Math Math Tutorials Geometry Arithmetic Pre Algebra & Algebra Statistics Exponential Decay Functions Worksheets By Grade Resources View More By Deb Russell Math Expert Deb Russell is a school principal and teacher with over 25 years of experience teaching mathematics at all levels. our editorial process Deb Russell Updated March 06, 2017 Definition: The bottom of a shape, solid or three dimensional object. The base is what the object 'rests' on. Base is used in polygons, shapes and solids. The base is used as a reference side for other measurements, most often used in triangles. The base is the surface of the object that is stands on or it is the bottom line. Examples: The bottom of the triangular based prism is considered the base. The bottom line of the trapezoid can be considered the base. Cite this Article Format mla apa chicago Your Citation Russell, Deb. "Definition of a Base." ThoughtCo, Aug. 26, 2020, thoughtco.com/definition-of-a-base-2312351. Russell, Deb. (2020, August 26). Definition of a Base. Retrieved from https://www.thoughtco.com/definition-of-a-base-2312351 Russell, Deb. "Definition of a Base." ThoughtCo. https://www.thoughtco.com/definition-of-a-base-2312351 (accessed January 21, 2021). copy citation