The list of values that an object supports is referred to as the SNMP Management Information Base (MIB). MIB can be used to describe any SNMP object or portion of an SNMP hierarchy.
The various SNMP values in the standard MIB are defined in RFC-1213, one of the governing specifications for SNMP. The standard MIB includes various objects to measure and monitor IP activity, TCP activity, UDP activity, IP routes, TCP connections, interfaces, and general system description. Each of these values is associated with an official name (such as sysUpTime, which is the elapsed time since the managed device was booted) and with a numeric value expressed in dot-notation (such as '1.3.6.1.2.1.1.3.0', which is the object identifier for sysUpTime).
See Supported MIBs for a description of the use of SNMP MIBs for Policy Management.