From WoWWiki

Medium Leather is used as a reagent in many professions.

Source

• It can be created by leatherworkers by combining four Light Leather.
• This leather can be skinned from beast and a few humanoid monsters ranging up to level 35.

As an ingredient

Medium Leather is used in the following recipes:

Leatherworking

• [Black Whelp Cloak]
• [Black Whelp Tunic]
• [Dark Leather Boots]
• [Dark Leather Cloak]
• [Dark Leather Pants]
• [Dark Leather Shoulders]
• [Dark Leather Tunic]
• [Earthen Leather Shoulders]
• [Fine Leather Pants]
• [Fletcher's Gloves]
• [Heavy Earthen Gloves]
• [Herbalist's Gloves]
• [Hillman's Belt]
• [Hillman's Leather Gloves]
• [Hillman's Shoulders]
• [Medium Armor Kit]
• [Nimble Leather Gloves]
• [Pilferer's Gloves]
• [Red Whelp Gloves]
• [Toughened Leather Armor]
• [Toughened Leather Gloves]

Tailoring

• [Reinforced Woolen Shoulders]
• [Spidersilk Boots]

Blacksmithing

• [Big Bronze Knife]
• [Bronze Axe]
• [Bronze Battle Axe]
• [Bronze Greatsword]
• [Bronze Mace]
• [Bronze Shortsword]
• [Bronze Warhammer]
• [Deadly Bronze Poniard]
• [Heavy Bronze Mace]
• [Heavy Copper Broadsword]
• [Iridescent Hammer]
• [Mighty Iron Hammer]

Engineering

• [Bronze Framework]
• [Deadly Blunderbuss]
• [Green Tinted Goggles]
• [Minor Recombobulator]
• [Portable Bronze Mortar]
• [Shadow Goggles]
• [Small Blue Rocket]
• [Small Green Rocket]
• [Small Red Rocket]

External links

Leathers
Generic	Ruined Leather Scraps • Light Leather • Medium Leather • Heavy Leather • Thick Leather • Rugged Leather • Knothide Leather Scraps • Knothide Leather • Heavy Knothide Leather
Special	Zhevra Leather • Thin Kodo Leather • Chimera Leather • Devilsaur Leather • Frostsaber Leather • Warbear Leather • Primal Bat Leather • Primal Tiger Leather • Core Leather • Enchanted Leather