Meat is a consumable item, available in all three Risen games. How it is obtained, however, as well as the effect of this item changes from one game to another.
Risen[]
Raw meat is only usable as a quest item for Rachel. Otherwise, it must be cooked using a frying pan over a campfire or stove, converting it into fried meat.
Fried meat can be consumed. Eating this will add 15 health to the character's total, never exceeding the maximum level of health available to him.
Risen 2 and 3[]
Raw meat is usable before it is cooked, increasing a character's regeneration by 10. This means that 10 points of health will be restored over time, rather than instantly.
Unlike in Risen, the character doesn't need to own any special equipment to cook raw meat; only access to a campfire or stove if required. All cooked meat is immediately converted to provisions. Once converted, it works as any provision (see that page for details).
(Fried) Meat can be looted from a table or chest. Once added to the character's inventory, meat is immediately converted to a provision, and works like all provisions do. Because of this, it is assumed "meat" is already cooked.
Acquisition[]
In Risen, raw meat can be obtained by killing various animals, such as boars or rats. Raw meat can be cooked at a campfire or on a stove (provided the character has a frying pan in their inventory).
Raw meat cooked in this manner is converted to fried meat. Rachel will also give you one fried meat each day, if you ask her (if you are not of another faction). Dargel in Harbour Town will also sell fried meat.
In Risen 2 and 3, raw meat can be obtained by killing creatures as well, such as rammers or armadillos. It can also be found as an item to take, such as from the hanging meat shanks at the house where Bran and Logan live.
Meat is only found as a lootable item, because all raw meat is converted to provisions once added to a character's inventory.