One's inner feelings or thoughts that are not shown outward; the true feelings inside a person.
彼女にはまだ言えない心の内がある。
She still has feelings she can't tell anyone.
彼は本当の心の内を打ち明けた。
He confessed his true feelings.
面接では、心の内を正直に話す必要はないこともある。
In an interview, there are times when you don't need to honestly reveal your inner thoughts.