UTM Stands for Unified Threat Management.  A UTM is a device that handles the security of your network.  In many cases it includes firewall, antivirus, intrusion prevention, spyware / malware protection, as well as content filtering.  A UTM is installed in place of a stand alone firewall and is able to filter network traffic before it reaches computers or servers on your network.  This can be a huge benefit as antivirus and firewall software can fail or get uninstalled on individual computers.