Estimator

A RV $T(s)$ of a sample. The calculated numerical value of the estimator (after the samples are found) is called the estimate.

Intuition

Parameter $(\theta )$	Estimator $(T)$	Estimate $(t)$
$\mu$	$\overline{X}$	$\overline{x}$
$\sigma$	$S$	$s$
Unknown constant	Random variable	Known constant