also: せいこう
Refers to the exact center of a target, or metaphorically to the crucial point or essence of a matter. Often used in the phrase 正鵠を射る (to hit the mark).
His remark hits the mark.
That question gets to the heart of the issue.
Standard kanji spelling. The reading せいこく is more common than せいこう.
Alternate reading. Less common but still encountered.
From Chinese 正鵠, where 正 and 鵠 both refer to the center of a target. The exact historical derivation is uncertain, but the compound is conventionally associated with the idea of a bull's-eye.