Load sharing is a defined policy of say, for the purpose of an example, sending one half of your network traffic towards one particular router or path, the other half to another router. You decide some goes one way, some another way.
Load balancing is sending all traffic across multiple paths, often dynamically and equally, and usually for the purpose of dynamically using aggregated bandwidth of the multiple links to avoid any one getting congested. This is sometimes used instead of failover when such multiple paths are available.
There are different ways of load balancing traffic e.g per destination where an entire flow of traffic will route down one path. Lets say you have two paths available and a huge ftp file to send. The whole file will go down one path. Start off another ftp a few seconds later and it will take the other (less utilised path). Things even out in this way.
Another is per packet where a single flow of traffic gets the round robin treatment across multiple links. Instead of routing down one path the packets that make up both ftp files would alternate between both links on a per packet basis towards their destination. More granular but not suitable for all types of traffic.
Thats my 10 cents. Hope this helps.
