Freedom rather than price
The GPL preamble distinguishes software freedom from price. Commercial distribution is possible while recipients retain specified rights to copy, modify and redistribute.
Version 2 and the 2007 version 3 are distinct texts, rather than names for a particular GNU program. A project’s licensing notice identifies the applicable grant.
Object code and corresponding source
GPLv3 defines source through the preferred form for modification, including required build and control material within its corresponding-source rules and exceptions.
Section 6 supplies several ways to accompany object-code distribution with source access. Their conditions differ; the text does not impose a universal duty to upload every private modification to a public website.
References: [2]
Versions and network interaction
An only-version grant differs from permission to use that version or later versions. Section 14 describes later-version choices; a new publication does not automatically relicense every older project.
GPLv3 distinguishes network interaction without transferring copies from conveying a work, and separately addresses combinations with GNU AGPLv3. The two licenses must not be treated as interchangeable.
References: [2]