Answer:

To interpolate means to estimate between two known numbers.

For example, suppose a girl’s height was 152 cm on 1st January last year and 156 cm on 1st January this year. A reasonable estimate of her height on 1st July halfway through last year is 154 cm.

When using the simple function to calculate new data points we usually do not receive the same result as when using the original function, but depending on the problem domain and the interpolation method used the gain in simplicity might offset the error.