A lead that positively attempts to establish tricks for the defence as opposed to a passive lead that simply intends to give no advantage to declarer.
Since both opponents have shown long suits, you expect declarer to have the wherewithal to make ten tricks given time. You therefore make an attacking lead from your short strong spade suit with the ♠6. If partner has the ♠A, you may be able to cash two or three tricks straight away. Even the ♠Q would be a good card to find, as then your lead sets up the king and jack.