Private laws affect a particular segment of the population, such as an individual, family, or small group.
This contrasts with public laws which are laws affect the country as a whole.
Private laws constitute only a small minority of the laws passed by Congress.
We cite private laws with the abbreviation Priv. L. No., which indicates that the law is a private law, followed by the number of the Congress which passed the law and the number of the law.
For example, Priv. L. No. 112-1 is the citation for the is the 1st private law passed by the 112th Congress.
You can view a chronological list of private laws passed by Congress here.