reg.exe is a process belonging to the Microsoft Registry Console Tool which is bundled with Windows. "This program is a non-essential process, but should not be terminated unless suspected to be causing problems. "
Non-system processes like reg.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that over time your registry suffers fragmentation and accumulates invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues