You can create any number of ticket types at Setup > EDIT Ticket Types.
If you want specific ticket types to not be available to the public, simply edit them and set them as disabled (uncheck the "Enabled" check-box).
Still, these ticket types are available for use by you or your team via the control panel. You can create orders, send RSVPs, Personal Invitations and Complimentary Tickets using these Ticket Types.
Note that you can customize badges, tickets and Passbook for each ticket type. So you might want to create different ticket types for volunteers, speakers, etc.
You can also group your ticket types at Setup > Ticket Type Groups