Definition
Semantic Versioning (SemVer) is a versioning scheme with the format major.minor.patch (for example 2.4.1): a major bump signals an incompatible API change, a minor bump adds backward-compatible functionality, and a patch bump fixes backward-compatible bugs.
How it works
When releasing, you increment the digit that matches the nature of the change. Package managers use these conventions to decide upgrade behavior — for example, automatically accepting patch and minor updates but never crossing a major boundary on its own.
Usage
Package ecosystems such as npm rely on SemVer to express compatibility ranges in dependencies (like ^1.2.3). Releases and changelogs are also described at this granularity.
Related and confusable terms
Release notes explain to users what happened in each version; SemVer defines what the version number itself means. Date-based or plain sequence numbers carry no compatibility information.