Question

what is meaning of sector

Answer 1

sector is a part from a circle which is cut at an angle of teta

Answer 2

see this figure , here shaded region is known as sector of circle .
actually , sector is the part of circle which inclosed by two radii and subtend some angle at the centre .

area of sector = angle suntend by arc at the centre (in °)/360° ×πr²

here in figure
angle subtend by arc at the center = ∅
and radius = R

, area of sector = ∅/360° × πr²