What is the purpose of a U.S. Social Security number, and who can apply for it?
A U.S. Social Security number is a taxpayer identification number, and only noncitizens with permission to work in the U.S. can apply for it.
Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the purpose of a U.S. Social Security number, and who can apply for it?

### Input: Not applicable

### Response:
A U.S. Social Security number is a taxpayer identification number, and only noncitizens with permission to work in the U.S. can apply for it.<|im_end|>