This is a reference to a blog post on MSDN.
Here’s the first paragraph from the post:
Range requests is the ability in HTTP to request a part of a document based on one or more ranges. This can be used in scenarios where the client wants to recover from interrupted data transfers as a result of canceled requests or dropped connections. It can also be used in scenarios where a client requests only a subset of a larger representation, such as a single segment of a very large document for special processing. Ranges specify a start and an end given a unit. The unit can be anything but by far the most common is “bytes”. An example of a range request asking for the first 10 bytes is as follows:
GET /api/range HTTP/1.1 Host: localhost:50231 Range : bytes=0-9