AJAX (Asynchronous JavaScript and XML) is a computer architecture, a web programming concept that combines several technologies: Javascript, JSON, and XML. This association has been thought to create more dynamic pages, to optimize the interaction with the user, and to bring more comfort of use.
Ajax is a technique compatible with the majority of web browsers (Google, Safari, Mozilla Firefox, etc...). It can be applied to all media: smartphones, tablets, computers, etc... whatever the operating system (Linux, Mac, Windows).