A dial plan essentially describes the number and pattern of digits that a user dials to reach a particular telephone number.

Route groups and route lists are thought of as hierarchical. You create your route group and add your route groups to route lists. Then you specify a route list or gateway to your route pattern. More descriptions on each below.

A route group allows you to designate the order in which gateways are selected. It allows you to prioritize a list of gateways and ports for outgoing trunk selection.

A route list associates a set of route groups in a specified priority order. A route list then associates with one or more route patterns and determines the order in which those route groups are accessed. The order controls the progress of the search for available devices for outgoing calls.

A route pattern/hunt pilot comprises a string of digits (an address) and a set of associated digit manipulations that can be assigned to a route list or a gateway.

All explanations are from this document:

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/4_0_1/ccmcfg/b03rtlst.html

Hope this helps!!