Definition
To have already learned or gained experience in something, which could be beneficial in the future.
掌握在身（未来可能有助益）
He already had a few years of relevant experience under his belt before starting the new job.
他在开始这份新工作之前，已经有几年的相关经验了。
Once you complete this project, you'll have another accomplishment under your belt to put on your resume.
一旦你完成这个项目，你的简历上就会多一个成就。
She has a master's degree under her belt, which is very helpful for her career advancement.
她已经取得了硕士学位，这对她的职业发展非常有帮助。