Beta Testing is the second phase of softrware or web trails during which a 'test' audience provides feedback about the user experience. Traditionally, alpha and beta testing are conducted in a controlled environment.
Today, beta testing is more of a pre-release strategy that is distributed to a wider audience. It is not only to 'test' the platform in a real environment, but to 'soft launch' a website or campaign as a preview to a target audience of key influencers.