Simple definition
An HTTP range request retrieves selected byte segments of a resource, useful for downloads and media seeking.
Purpose and use
A Range request asks for one or more portions of a representation, for example to resume a download or retrieve part of a media file.
How does it work?
An accepted range can produce 206 Partial Content with Content-Range. The server may instead ignore the request and return the full representation.
Example and verification
When resuming, check status, returned range and resource version before combining bytes with an existing partial file.
Points to watch
An unsatisfiable range can produce 416. Combining segments from different versions can create an inconsistent file.
In short
Range supports partial transfer when supported by the server and intermediaries; version consistency remains essential.