noun
awareness of the world; understanding of things; judgment; discretion
Refers to the cognitive ability to perceive and judge one's surroundings, often used in the phrase 物心がつく (to reach the age of awareness).
物心がついたときから、彼は動物が好きだった。
He has liked animals ever since he became aware of the world around him.
まだ物心のつかない幼い子どもには難しい話だ。
It's a difficult story for a young child who doesn't yet have awareness of things.