A cow is an animal in The Sims 2. Sims can interact with the cows in the field, as you have the option to milk the cow, give a gift or tip the cow over. All of these interactions are used for something at some point during the game.
By milking a cow, you recieve a glass of fresh milk. However, if you tip the cow before milking it you will end up with a milkshake. Furthermore, if you give the cow chocolate via the give gift interaction and then milk it you will recieve chocolate milk, and if it is tipped as well you get chocolate milkshake. All of these products can be sold in the Store for a small amount of simoleons.
There are two cows in the cow field in the Town Square and one bull. The bull cannot be interacted with in any way and is purely there for decoration. Cows do not stray from the field however sometimes glitches can occur which causes them to appear in other places.
At the edge of the cow field is a shed which has been rumored to contain things such as a secret passage, extra storyline and even the missing Honest Jackson. These claims are all false.
Cows also serve as a theme in part of the game, as Ava Cadavra asks you to excavate the Bovine Shrine for her, a shrine dedicated to cows. The "leader", the Prime Heifer is a statue in the centre of the shrine. It is unknown why Ava liked to wordship cows as it is never really explained. Whilst completing some of the goals, there's an interaction to take the bell from one of the cows to give to Ava.