I think wiki.answers answers it best. It is the protection, preservation and careful management of our natural resources. And in Physics case the 'conservation of momentum' is an objects stopping distance, in proportion to its velocity and mass. In other words conservation means using resources in the environment carefully. The idea that over a system, a specific value is held constant such that any change to the system can neither add nor subtract to that value.
Conservation means to me the management and preservation of our natural resources. As individuals we all play a role in the total involvement of our environment. What we do on a daily basis changes the Earth for our future, may it be good or bad. Let's work together and keep our environment clean for our future children.