Short for end user license agreement, EULA or a UA (user agreement) is a contract between the buyer and seller of proprietary software that describes the purchaser's rights. For example, an EULA lets a person know whether or not they can copy and redistribute the software after buying or, how many of their devices can share it. Though some still exist in physical form, the vast majority of EULAs are displayed as a click-through digital contract with terms users must agree to upon installation. The user will be required to click "Accept" or a "Disagree" button or check a box that says he or she accepts or disagrees with the agreement.
Tip: If you're like most people who don't like the thought of reading a license agreement, but want to make sure you're not agreeing to anything bad, try the EULAlyzer. This utility that can analyze and summarize any EULA for you.