In music notation, a sixteenth rest is a pause in the music lasting for one-quarter of a beat, the same duration as a sixteenth note. It is drawn as an eighth rest with a second flag in the middle of the staff.
On the staff, a sixteenth rest looks something like this:
/\
---| /-----------------------------------------------------
|/
---/------------------*-/----------------------------------
/| *-/
-/-|/\----------------/------------------------------------
| | | /
|--|--|----------------------------------------------------
\ | |
--\|_/-----------------------------------------------------
|
\|