Harvard University on ADR : It refers to a variety of processes and techniques designed to help disagreeing parties come to an agreement short of litigation. These processes can include everything from facilitated settlement negotiation, in which disagreeing parties are encouraged to consult directly with each other prior to some other legal process, to arbitration, which can look and feel very much like a standard trial. The most commonly used ADR systems are negotiation, mediation, collaborative law, and arbitration.

https://hls.harvard.edu/dept/opia/what-is-public-interest-law/public-interest-work-types/alternative-dispute-resolution/