Definition
Officially registered as an employee of a company or a member of an organization, society, sports team, etc.
在册（受雇）
The software company currently has over five hundred employees on the books.
这家软件公司目前有超过五百名员工在册。
Our club currently has over two hundred members on the books.
我们的俱乐部目前有超过两百名会员在册。
Even though he hasn't played in a while, he is still on the books as a player for the team.
尽管他已经一段时间没有上场比赛了，他仍然是球队的注册球员。