Stirrups is a technology in Age of Empires II: Definitive Edition that is unique to the Bulgarians and can be researched at the Castle. Once researched, it increases the attack speed of the Scout Cavalry line, Knight line, and Konniks by .
Note that Dismounted Konniks are unaffected by Stirrups.
Mounted Konniks have the slowest melee attack of a cavalry unit in the game; however, after researching it, their attack rate drops to that of a Knight (1.8), while having a higher base attack than Knights, so in the Castle Age, this technology is a must if the player wants to utilize them, though it is quite expensive and Blacksmith technologies should still be prioritized first. In the post-Imperial Age, Elite Konniks attack faster than generic Paladins. This, combined with their easy creation and and being able to fight dismounted, make the Konnik one of the best cavalry units in the game, as well one of the finest unique units.
Stirrups also affects light cavalry, which puts their Hussars at a huge advantage in "trash wars" as well performing extremely good at raiding and killing Villagers, and probably makes a fully upgraded Bulgarian Hussar the strongest in the game and able to defeat generic Hussars, Mongol Hussars, and even Malian Light Cavalry with Farimba in one-to-one combat.
After update 36906, to compensate for losing access to Paladins, Stirrups was changed to affect the Knight line as well, and as a result, Bulgarian Knights become one of the most dominant units in the Castle Age, excelling at assaults and able to stand up against even Camel Riders and Pikemen, and Bulgarian Cavaliers when fully upgraded have the highest potential damage per second among the cavalry units in the game (excluding elephants), even outperforming Lithuanian Paladins with 4 Relics collected (~11.85 damage per second vs 11.6) and Malian Cavaliers with Farimba.