You sure that wasn't a missprint and really said "Center Tap".
If it's center tap you can think of it as additional secondary Taps to pull
off multiple voltages.
For intance below it has a tap in the center, where you have a voltage across
AB, BC, and AC.
Could be 12V, 12V, and 24V.

       -------3       3------------------------- A
                3       3_____ B
                3       3
     -------- 3       3-------------------------- C
    Primary,

Regards,
Dan