In music notation, a fermata is a half-circle with a dot in the center positioned over a note, just above it or the staff (whichever is higher). It indicates that the note should be extended past its specified duration for an indeterminate length of time. The word means "stop" in Italian.
For purposes of counting beats, the measure containing the note counts it as if the fermata were never there. It is used only to add style and feeling to a particular point in the music, not extend the number of beats in a note. When followed by a fetura, it should be terminated abruptly.
A fermata looks something like this, when positioned above a half note on a staff:
_
/\ /.\
---| /-----------------------------------------------------
|/
---/---------------------------O--------------------------
/| |
-/-|/\------------------------|----------------------------
| | | |
|--|--|-----------------------|----------------------------
\ | |
--\|_/-----------------------------------------------------
|
\|