In music notation, a quarter note represents one beat and is represented by a filled circle with a stem. It is so named because it lasts for the duration of one quarter of a whole note. Also called a crochet.

A series of quarter notes on the staff looks something like this:

    /\                                                     
---| /-----------------------------------------------------
   |/                              |                       
---/------------------*------------|-----------------------
  /|            *    |      *      |                       
-/-|/\---------|-----|-----|-------|-----------------------
|  |  |        |     |     |      *                        
|--|--|--------|-----|-----|-------------------------------
 \ |  |        |           |                               
--\|_/-----------------------------------------------------
   |                                                       
  \|