This is the 2740th most frequent Chinese word.
劲
"劲" means strength, energy, vigor, or force.
Here, '劲' is used as a noun referring to 'effort'.
他干活特别卖劲，总是完成得很好。
He works with great effort and always completes tasks very well.
In this context, '劲' means 'spirit' or 'excitement', reflecting an emotional state.
听到这些好消息，我心里劲满了。
Upon hearing this good news, I was filled with spirit.
In this sentence, '劲' is used as an adjective meaning 'strong'.