VTP stands for VLAN Trunk Protocol. VTP is used to propagate VLAN cconfiguration. VTP advertisements are multicasted. They are sent every 5 minutes or whenever there is a change in VLAN configuration. VTP revision number is included in these advertisements. Whenever a client receives a VTP advertisement with a higher revision number, the client will update its vlan configuration with the vlan information being advertised.
There are 3 modes:
VLAN cannot be edited on a switch operating as a client.
VLAN can be edited on a switch operating as a server. This information is propagated to the switches operating as clients.
VLAN can be edited on a switch operating in transparent mode. However, these changes are not propagated. Switches operating in transparent mode do not update their configuration based on advertisements from the switch operating in server mode. All change are local for a switch operating in transparent mode.