Any of various systems of reckoning time in which the beginning, length, and divisions of a year are defined, sometimes along with multiyear cycles.

A Calendar is a thing were you can write down what you have to do like go shopping or if you are going to a party or something, I don't know. It will help you remember what to do everyday so in my opinion get a calendar!

A set of pages that show the days, weeks, and months of a particular year, that you usually hang on a wall.