Simple definition
udev manages Linux device events and dynamically creates device nodes and symbolic links.
Purpose and use
udev handles device events in userspace and applies rules for properties, permissions or persistent links.
How does it work?
Kernel events are matched against rules to prepare usable device representations.
Example and verification
When naming is unexpected, compare device properties, active rules and associated events.
Points to watch
A name such as /dev/sdX can change between boots; an overly broad rule can also affect multiple devices.
In short
Stable device properties reduce naming ambiguity.