Too many to count; innumerable or countless.
夜空には無数の星が輝いていた。
Countless stars were shining in the night sky.
彼の経験には無数の失敗も含まれている。
His experience includes countless failures as well.
図書館には無数の本があり、選ぶのに迷った。
There were countless books in the library, and I couldn't decide which to choose.