A photoinitiator is a chemical compound that is used to initiate the process of photo-polymerization in the presence of light. There are several other words that can be used as synonyms for photoinitiator, including photosensitizer, actinic initiator, and photosensitizing agent. These terms are often used interchangeably to describe the same type of compound that is used in the production of adhesives, coatings, and other products that require rapid curing. Additionally, other related terms include photoactivators, photoreactors, and photopolymerizable materials, all of which refer to various aspects of the photo-polymerization process that is initiated by photoinitiators.