Q.An estimator is sample statistics used to estimate a :

Estimation uses a sample statistic to infer an unknown population parameter. A point estimate (e.g. $\bar{x}$ for $\mu$) is a single best-guess value; an interval estimate (confidence interval) gives a range, with a stated confidence level, expected to contain the true parameter:

$\bar{x} \pm Z_{\alpha/2}\cdot\dfrac{\sigma}{\sqrt{n}}$ …