What Is Meant by the Term, Midterm Congressional Elections

What is meant by the term, midterm congressional elections?

A) elections that are held in presidential election years
B) elections that parties hold in order to nominate candidates to run for office
C) elections held by Congress to nominate presidential appointees
D) elections held midway between presidential elections, for all House seats and one-third of the senate seats
E) elections held at the local level for municipal and special district elected offices