A motivational speaker or inspirational speaker is a speaker

Public speaking

Public speaking is the process of speaking to a group of people in a structured, deliberate manner intended to inform, influence, or entertain the listeners...

 who makes speeches intended to motivate

Motivation

Motivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...

 or inspire an audience. In a business context, they are employed to communicate company strategy with clarity and help employees to see the future in a positive light and inspire workers to pull together.

There are similarities between motivational speakers and inspirational speakers, and someone could be labeled as both simultaneously, but they are not necessarily interchangeable.