The PLRA is a U.S. federal law enacted in 1996 during the Clinton administration that makes it harder for prisoners to file lawsuits in federal court. It has made an enormous negative impact on the efforts of jailhouse lawyers fighting very serious battles that would already be extremely difficult without this huge barrier in place.
ACLU Fact Sheet: Explains Exhaustion of Administrative Remedies, Filing Fees, Three Strikes Provision, and the Physical Injury Requirement
Jailhouse Lawyers Manual Chapter 14: The Prison Litigation Reform Act – an extensive overview that is part of the book published by the Columbia Human Rights Law Review which is used by many in prison
Prison Grievances: A graphic novel that explains the procedures for filing grievances, the website promoting it gives a lot of information about what prisoners need to know with regard to the PLRA