You hold …

North
♠ A 4
♥ A Q 2
♦ 8 3
♣ A K Q 8 6 2

And the bidding proceeds …

South  North
1♠       2♣
2♥       3♣
3♥       ?

North would like to blackwood at this point but has a diamond problem ~ the unbid suit. A fun solution for this hand is to bid 5♥ which asks partner for a control (1^st or 2^nd) in the unbid suit ~ Diamonds!

South
♠ K Q 10 7 6
♥ K 8 7 5 4
♠ Q 5 4
♣ —–

South  North
1♠       2♣
2♥       3♣
3♥       5♥
Pass

South would pass 5♥ ~ denying 1^st or 2^nd round control of diamonds.

via Play Better Bridge.