Commercial paper is typically offered by very large companies and is not necessarily invested into by a smaller investor. The reason for this is that usually the minimum investments are $100,000.
Commercial paper is, in simple definition, an unsecured promissory note. Usually these large companies are raising capital in this manner versus borrowing from a bank(s). They are seeking this capital usually to meet short-term debt obligations of the company. Because it is not secured with collateral, typically the only companies selling commercial paper are companies with outstanding credit ratings. The commercial paper is sold at a discount from its face value.