Adventist Youth Honors Answer Book/Music/Note duration
The names of the types of notes come from the fraction of a measure that each note gets in bar of music in four four time. In the 4/4 time signature, the top 4 indicates how many beats are in each bar of music, and the lower 4 indicates that a quarter note gets one beat. Since four quarter notes would fill the entire bar, they are called quarter notes. A half note would get two beats, or ½ of the measure, and a whole note gets 4 beats or the whole measure.
Quarter notes have a solid note head with a stem attached.
Half notes have a hollow note head with a stem attached.
Whole notes have a hollow note head, but no stem at all.