In mathematical analysis, the maximum and minimum[a] of a function are, respectively, the greatest and least value taken by the function. If you say that something is a particular amount maximum, you mean that this is the greatest amount it should be or could possibly be, although a smaller amount is acceptable or very possible. Maximum definition: An upper limit permitted by law or other authority. MAXIMUM definition: 1. being the largest amount or number allowed or possible: 2. the largest amount allowed or…. Learn more. Definition of maximum noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. The meaning of MAXIMUM is the greatest quantity or value attainable or attained. You use maximum to describe an amount which is the largest that is possible, allowed, or required. MAXIMUM definition: the greatest quantity or amount possible, assignable, allowable, etc. See examples of maximum used in a sentence. Both a noun and an adjective, maximum takes it to the max: it means the most, the fastest, the biggest. MAXIMUM meaning: 1. being the largest amount or number allowed or possible: 2. the largest amount allowed or…. Learn more.