what does this symbol mean?(like a comparator,but there is another symbol in this triangle)
It is a comparator with hysteresis. Here is a diagram from this Maxim datasheet



When the output is in the high state the voltage required to drive it low (B) is higher than the voltage required to drive it high again (F), so for input voltages between F &amp; B the output will be in either one state or the other, depending on the history of input voltage. 

By incorporating hysteresis, a noisy signal can be "cleaned up" as the output will not transition many times for small changes in input voltage.