In Physics, intensity can usually be understood as the strength of something like a beam of light. To figure out (i.e., compute) the exact intensity of a beam of light or a fire hose spraying water, we need to know how many units of light or water are coming to some area in some period of time. A factory might have an "intensity" of 100 cars per day delivered to the loading dock. A fire hose might have an intensity of 100 buckets of water per minute per open window of a certain size in a burning building. 