Federal Elections are for:
Midterm Elections mark the halfway point of a Presidential term. Midterm elections decide members of Congress, but not the President. As House and Senate seats are two-year and six-year terms, respectively, midterm elections decide all House seats and one-third of Senate seats. Midterms, while not as popular as Presidential elections, decide which political party will control the House and the Senate for the next two years.
Many state and local elections happen at the midterm, as well.