how to measure wing sweep angle??

How is the wing sweep angle measured.

according to the the definition by wiki
" the angle between the perpendicular to the design centreline of the
wing in the wing plane, and either the leading edge or ¼ chord line"

what is this 1/4 chord line??
can anyone explain it to me in simple terms

When an airfoil is drawn in profile the line from the forwardmost
point to the rearwardmost point is the chord line. The quarter-chord
point is a quarter of the length back from the leading edge. Plot the
quarter-chord points all along the wingspan in plan view and you have
the quarter-chord line (which may not be a straight line, making the
determination of the sweep angle problematic in such cases).