Short for Network Operations Center.
The Internet has matured. The NOC has taken on the role of central monitoring and coordination for systems grown more complex than single server or network link monitoring. Alerting systems inform employees of the NOC of low disk space, systems that have failed to respond, and larger than ordinary latency from web servers. Systems such as Nagios forward these alerts to massive dashboards in the central NOC, where highly trained system administrators perform triage.
With the advent of widespread virtualization and clustering, engineers working in this environment are broadly specialized individuals. Talents required for these roles include systems knowledge of Linux, Windows, VMWare, TCP/IP, web servers (Apache, generally), and some knowledge of scripting in order to do heavy lifting. It requires sysadmin cool as a prerequisite - there are no NOC jobs exempt from a paging schedule that places employees oncall in case of alerts.
Networking has increased in complexity from the late 90s to early 00s. Telecommunications means monitoring the health of routers, switches, and content delivery networks such as Akamai. In the case of companies operating their hosting infrastructure on cloud service providers such as Amazon Web Services or Rackspace, this may require more specialized knowledge that dovetails with Development Operations (DevOps) skillsets.