A uniform field is that in which th

A uniform field is that in which the electric field is constant throughout. Just like the so-called "frictionless surface" in mechanics, the uniform field is an ideal but unreal situation that makes for simpler calculations. Equations involving non-uniform electric fields require use of differential calculus.

Source: Boundless. “Uniform Electric Field.” Boundless Physics. Boundless, 27 Jun. 2014. Retrieved 18 Dec. 2014 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/electric-potential-and-electric-field-18/overview-139/uniform-electric-field-501-6060/