Question

define oscillation amplitude and time period......

Answer 1

time period  
the time taken to complete one oscillation is called the time period of the simple pendulum.

Oscillation :
The change in density from one maximum value to the minimum value and again to the maximum makes one complete oscillation.

amplitude
The maximum displacement of a points on a wave is called Amplitude
Meters is the unit of amplitude.

Answer 2

The to and fro motion of a simple pendulum is called an oscillation. One oscillation involves the bob moving to both extremes and returning to its mean position.
The maximum displacement of the bob from its mean position is called amplitude.
The time taken to complete one full oscillation is called time period of the pendulum.