Each priority in the dialplan calls an application. An application does some work on the channel, such as answering a call or playing back a sound prompt. There are a wide variety of dialplan applications available for your use. For a complete list of the dialplan applications available to your installation of Asterisk, type core show applications at the Asterisk CLI.
Most applications take one or more parameters, which provide additional information to the application or change its behavior. Parameters should be separated by commas.