It is the total rate of fuel used by our body or the total calories burned when we are not doing anything or just resting.
Resting Metabolic Rate is affected by some factors such as our age. As we become older, our muscles deteriorate and it leads to lower RMR. As a result, aging is accompanied with gaining of weight.
We can not assure that dieting or any other form of doing exercises will really help someone to loose weight. We only get short-term results but what about the long-term? We know a fact that the future is more important than the present. Weight loss may mean losing your muscles instead of losing your fats. So, if you think of loosing weight you may get the other-way-around results, because muscles are essential for metabolism. Choosing a more effective exercise really matters. Weight lifting is commendable.
As you take steps in increasing your RMR, you are pushing your self on your way to a lighter weight and healthier life as a whole.