i-adjective
Emphasizes that something is too numerous to count. Often used in literary or emphatic contexts.
夜空には数知れない星が輝いている。
Countless stars are shining in the night sky.
彼は数知れない困難を乗り越えてきた。
He has overcome innumerable hardships.
Compound of 数 (kazu, 'number') + 知れない (shirenai, 'cannot know'), literally 'cannot know the number'. The exact historical derivation is uncertain, but the phrase is conventionally associated with the meaning 'countless'.