https://fedoraproject.org/wiki/Packaging:Guidelines#.2Frun suggests that /var/run is something separate from /run. This is misleading. Suggested rewording below.

Old text:

System services may need to store run-time variable data somewhere before /var/run is mounted. Currently, many programs are abusing /dev for that purpose. A few distributions have figured out elaborate hacks to use /var/run even before /var itself is mounted to do this. These are seen as less than ideal, however. Several major distributions have committed to support using /run for this purpose instead.

For now, applications can use /run or /var/run almost interchangably. /run MUST be used when the application can be started during boot before /var may be mounted.

Suggested rewording:

System services should store small volatile run-time data in /run. It is a tmpfs backed directory that is mounted in very early boot, before any services are started (and before /var is available). /var/run is a legacy symlink to /run.