Frequency = 2 cycles per second
Period = 0.5 seconds
The period of a wave is the time it takes to go through one complete oscillation or cycle. The term "vibration" could also be used.
Thinking of a pendulum, imagine that it starts from the left side. The period will be the amount of time it takes to swing over to the right and come back to the starting position.
In this case we know that 10 cycles take place in 5 seconds.
The frequency is just the inverse of this; the number of cycles per second.