Theory and Conventions
M J Bridge
Voidwood or Exclusion Blackwood (sometimes incorrectly referred to as Lackwood)
These are two different names for the same thing.
Strictly speaking the third name refers to a similar convention which is scarcely seen any more, but the term is not infrequently used as an alternative for the present convention.
Using this convention, once a suit has been agreed then a jump in a new suit shows a void and asks for key-cards on the usual scale but not counting the ace of the void suit.
K Q J 5 2
A K Q 6
K Q 9 8
3♠ is a limit raise.
All you need to know about are the aces in diamonds and spades.
Bid 5♣ which asks for precisely this information.
Note that a standard Blackwood response showing two controls would not be helpful.
This convention is strongly recommended as you look to move beyond an intermediate standard.
Post intermediate and above