See the image (Part a). It is level triggered. Meaning, trigger can happen anytime during the high clock level. See the image (Part b and c). It is edge triggered. Trigger can happen only during the edge of the clock.
Hence, it is quite clear that in a level triggered circuit, output can change several time (because a more time is allotted for the change to occur.).
Example: In level triggered, say, between 2ms and 4ms, a circuit can trigger many times. Whereas, in edge triggered circuit, between 2ms and 2.0001 ms, changes are that circuit will trigger atmost one time.
