Why do Rivers Curve?

Rivers become curvier and curvier until they bump into themselves. Then, lakes follow the route of least resistance and connect to form a straighter route. What’s left over is called an Oxbow lake… but they go by a lot of different names. In Australia they are referred to as Billabongs; in South Texas, they are called resacas, sometimes they are called ‘horseshoe lakes’. Do you have a special term for them in your country?