It is similar to Blackwood but uses 4 instead of 4NT as an "asking bid" to inquire about the number of aces held by partner; a further asking bid may follow to inquire about the number of kings held.
It is similar to Blackwood to inquire about the number of aces. These aces are held by partner. It uses 4 instead of 4NT as an "asking bid" to inquire about the number of aces. These aces are held by partner. A further asking bid may follow to inquire about the number of kings. These kings are held.