Alphanumeric
Refers to pagers that use both numbers and text to relay messages.

Dedicated alpha entry terminal
A business can purchase one to be used with multiple alphanumeric pagers. Used primarily by companies that need to send text messages to numerous pagers at once.

Numeric
Refers to pagers that use numbers only to relay messages.

PCS
Personal Communications Services. A broad range of individualized telecommunications wireless services consisting of voice, data, and video applications that enable people or devices to communicate independent of location.

PIN number
Personal identification number (yes, it's redundant). This number corresponds to a particular pager and is used for identification purposes so that messages get to the right places.