feel at ease; feel relieved; feel comfortable
Describes a state of mental relief or comfort, often after a worry or burden is removed. Commonly used in the form 気が楽になる.
I felt relieved after the exam was over.
I felt better after talking to him.
A set phrase combining 気 (spirit/mind) and 楽 (ease/comfort). The exact origin is uncertain, but it follows a common pattern of describing mental states with 気が + adjective.