Taps AKA Directional Couplers or Multi Taps is a passive electronic device used to distribute television signals. A tap is used to "tap off" a part of the available signal and send it to a TV or multiple TV's. Taps are directional (Directional Coupler) to prevent unwanted signals from being fed backwards in a system.
Taps are available in one, two, four eight and twelve port models. Most common tap values are 4,8,11,14,17,20,23,26,29 and 32 dB. Some manufacturers call a 4 dB tap a 3 dB tap or an 11 dB tap a 12 dB tap. These taps are actually the same with specifications being practically identical.
Taps have an input port, an output port (or ports). Depending on tap value the tap port will tap from 3 dB to 32 dB off from the input level while only reducing the output level from 3 dB to 0.7 dB. This is what makes taps very efficient in distributing TV signals.