The crossword solution for the term 'Half of a Vacation Rental App' is AIR, which stands for 'Application Interface Runtime'. AIR is a software framework developed by Adobe Systems that enables developers to create applications that run on multiple operating systems. It is used to create applications for mobile devices, desktop computers, and web browsers. AIR is also used to create games and other interactive experiences. AIR is an important part of many vacation rental apps, as it allows developers to create applications that can be used across multiple platforms.