Horse tack are items that Henry can equip his horse with, and includes horse head armour, body armour, cover, bridle, saddle and horseshoes. Henry cannot wear them, as he is a man, and not a horse.
Horse head armour[]
Horse head armour is worn by your horse and increases its defensive stats, but may occasionally decrease speed.
Body Armour[]
Body Armour is a category of horse tack. At this point there is no known horse body armour in the game, although there is a spare inventory slot on your horse. This is primarily for the use of modders.
Cover[]
Covers, also called caparisons, are a category of horse tack that can be purchased from the Horse Traders.
Bridle[]
Bridles are worn by your horse and give them more courage.
Saddle[]
Saddles increase the load capacity of your horse, meaning they can carry more weight, but decreases their speed.
Horseshoes[]
Horseshoes increase the speed of your horse.