A leader's job is to lead a team, by improving relationships, handling HR and project related tasks.

They are differentiated from lead designers, who are not leaders, but designers that lead the overall construction of a project, but not the entire team.

A task is a job that usually has a card in the right side of the UI. It can be a contract to create some software, the alpha phase of the player's own project, a lawsuit, etc.

Work items and tasks can be used interchangeably in most cases, but work items refer to the actual UI element, so tasks is more general.

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).