In music notation, a half note represents two beats and is represented by an open circle with a stem. It is so named because it lasts for the duration of half of a whole note. Also called a minim.

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

    /\                                                     
---| /-----------------------------------------------------
   |/                              |                       
---/------------------O------------|-----------------------
  /|            O    |      O      |                       
-/-|/\---------|-----|-----|-------|-----------------------
|  |  |        |     |     |      O                        
|--|--|--------|-----|-----|-------------------------------
 \ |  |        |           |                               
--\|_/-----------------------------------------------------
   |                                                       
  \|