An LMS is short for Learning Management System. It is a software that allows you to automate, manage, and capture the learning, or training, with your organization.
An LMS, or learning management system, combines a wide range of features to present a class setting without having the students come into a physical classroom. It all depends on the WordPress LMS plugin you go with, but in general, the tools allow you to create classes, share coursework, enroll students, and evaluate the students with quizzes.