This is a great question. Perhaps the most important point to keep in mind is that the world of business is not monolithic. Each company differs. For this reason, it is hard to say what each companies' structure is. With this said, generally speaking task forces, teams or project managements have two points in common.
First, they are temporary in nature. In other words, these groups are created for a specific period of time to finish a given task. From this perspective, we can say that these groups are not perpetual like the permanent positions in a company like human resources, accounting, and the like.
Second, these groups are created in view of a certain need that a company has. For example, if a company feels as though that they are paying way too much on insurace, then they may assign a task force to explore why this is so and how they can cut costs. After a given time, they will report back to the executives of a company and give their assessment. Hopefully, through this task force, the company can save money.
Here is another example, if a company is faced with an accounting problem, they may do the same by assigning a team to investigate the accounting problems.