Foundations
Semantic Versioning
Also: semver
A convention that writes versions as major.minor.patch, where patch is for fixes, minor adds features and major may break compatibility.
In more detail
Versions are compared part by part as numbers, so 0.31.0 is newer than 0.7.3. Many projects follow the convention and some do not, so read the project's notes. Security fixes often ship as patch releases, which makes staying current on the patch level a cheap protection.