Like cross-platform program, means one that can run across multiple computer platforms, a cross-browser refers to the ability of a website, HTML construct, application or even client-side script to work in several different environments, ones that provide its required features. So the websites having the features of cross-browsing can runs on several browser.
Cross- browsing ability is important because the availability of wide range of devices, Operating Systems(OSs), browsers makes developers and designer to create a website that can run independently. So in development of software cross browsing testing becomes an important part. To get a consistent experience and behavior across all devices, platforms and browsers the testing is crucial