What it means

1. noun the period of time that it takes for a planet (as, e.g., Earth or Mars) to make a complete revolution around the sun
   “a Martian year takes 687 of our days”
2. noun a period of time containing 365 (or 366) days
   “she is 4 years old”
3. noun a period of time occupying a regular part of a calendar year that is used for some particular activity
   “a school year”
4. noun a body of students who graduate together
   “the class of '97”