What is a Browser?
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web.

An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to related resources.

Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or files in file systems. Some browsers can be also used to save information resources to file systems.
The street interview: What is a Browser?
Google's explanation of what a Browser is