Employees are leaders, designers, artists, programmers, support, lawyers or accountants. People who are occupied with directly adding value to the company. Employees will spend their day sitting at a computer to work.

The term differentiates itself from staff, who are occupied with keeping operations running smoothly so the employees can work, e.g. cleaners, cooks, maintenance, etc.

HR refers to human resources. HR is a series of options you can enable on a team in the game, based on the skill of the leader, to automatically manage education, hiring, complaints and salaries.

It is assumed to be abbreviated in the UI in most cases, so if you write it out as human resources every time, it might be cut off in a lot of places. It would be preferable to find an abbreviation or at least a very short-form of the word(s).