Vocabulary
눕다
lie down / be lying
Meaning
Verb 눕다: to lie down; the form here is 누워.
Why this form?
앉다 — sit: a seated posture rather than lying down.
Relevant irregulars
눕다 → 누워: ㅂ-irregular conjugation.
Forms not to confuse
앉다
의자에 앉아 있어요. — I am sitting on a chair.
Examples
얘가 누워 있는 걸 봤어요. — I saw him lying down.
침대에 누워 있어요. — I am lying on the bed.