Flatness (mathematics) definition

(1) Inactivity; showing an unusual lack of energy

"The general appearance of sluggishness alarmed his friends"

(2) The property of having little or no contrast; lacking highlights or gloss

(3) The property of having two dimensions

(4) A deficiency in flavor

"It needed lemon juice to sharpen the flatness of the dried lentils"

(5) A want of animation or brilliance

"The almost self-conscious flatness of Hemingway's style"