Void-showing, asks for key cards excluding the void suit.
Exclusion Blackwood is a jump shift when cue-bidding (e.g. 1S-3S-4C-5H, 1S-3S-5C)
or a jump higher than a splinter.
An unnecessary jump is...
A splinter if it's below 4 of the agreed trump suit.
(If it were possible to splinter at two levels, then the higher one would be void-showing... but I don't think it is.)
It's Exclusion Blackwood if it's between 4 and 5 of the agreed trump suit.
It's a complete two-suiter if it's at the 5-level and above the agreed trump suit.