In uk.d-i-y, BraileTrail wrote:
Could someone please explain the difference (and significance) of gangs
and ways as they are used in lighting circuits.

"Gang" means the number of separate physical switches sharing the plate.
So, your boggest-standardest lightswitch controlling just one light is
"single gang"; the thing you have in a room where one plate has a switch
for the central light and a separate switch for the wall lights is "two
gang" or "double gang"; one with three switches on the one plate is "three
gang".

"Ways" is a separate concept, describing the number of distinct, active
current paths provided. For a simple on-off function, you need just one
current path which is either open or closed - that's a "1-way" switch.
When you want to switch from two different places, you need a "2-way"
switch, which connects one of two separate terminals to a common terminal
depending on the switch position. 1-way and 2-way is all you'll ever come
across in domestic mains switches, with the exotic exception of an
"intermediate" switch, used in between 2-way switches to give you
switching at more than two different placeses.

A 2-way switch can always be used in place of a 1-way: you wire to the
Common and L1 terminals, ignoring the L2 terminal. (Or to the Common and
L2 terminal, and then mount the switch upside-down ;-) Mass production
and stock-holding costs mean you'll often find only a 2-way flavour
available anyway.

HTH - Stefek