What does estimated mean in math?

Answer 1

To make an educated guess. for instances if you were asked to estimate half of 1426, you would round down to to 1400, and half that which is much easier.

Half of that that is 700, therefore you would estimate the answer to be around 700.

Answer 2

It means an approximate value that is calculated rather than an exact value. A value may be estimated because it is quicker or simpler to estimate an approximate value or because there is simply no way to obtain the true value analytically.