What is EULA it?

I believe you are asking about the abbreviation for "End User License Agreement," which is a common terminology in IT (information technology). It refers to the licensing of software. A "EULA" is a legal contract, made between the author (or publisher) of a software application and the user of that application. It can also be called a "software license." The EULA is similar to a rental agreement.

By signing the EULA, the user agrees to comply with the terms of usage and the restrictions stated in the contract. For example, if you purchase an Apple product online, you will have to accept the company's terms of usage, such as agreeing not to make other copies of the software, nor trying to alter it in any way; failure to comply could result in the company suing you. I enclose a typical EULA so that you can see what terms and conditions the user must accept.