Definition:
A/B Testing is a simultaneous experiment conducted between two variants A and B to determine which performs the best or converts more. This test can be conducted with as many variants as possible, despite the name A/B testing.
This technique is used in web analytics to weigh the traffic and analyze the statistics of two or multiple pages. In this test, we can compare two versions of single variable to determine the most effective variant, which has identical features except one or two different features. A/B testing is considered to be performed continuously on anything, it is especially performed in marketing analysis and most of the marketing automation software comes with the pre-loaded A/B testing features.
Further Reading:
Book :The Lean Startup by Eric Ries