Load balancing is a computer networking methodology to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid overload. Using multiple components with load balancing, instead of a single component, may increase reliability through redundancy. The load balancing service is usually provided by dedicated software or hardware, such as a multilayer switch or a Domain Name System server. (wikipedia)
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Load balancing is implemented as equal cost multipath routing. With load balancing two or more gateways can be specified for the same destination. That applies to the default one as well. Equal cost multipath routes can be created by routing protocols (RIP or OSPF), or by adding a static route with multiple gateways. The routing protocols may create routes with equal cost automatically, if the cost of the interfaces is adjusted properly. (http://www.mikrotik.com/solutions.php)
