I heard someone mention this the other day, and, having also learned about these two kinds of pollution in my Environmental Economics class, I figured that it would be nice to expound upon them for a little while. Point source and nonpoint source both refer to different categorizations of what has been termed "pollution" - in this case, we're just discussing pollution resulting from modern industrialism. While pollution can be worldwide, regional, or very localized in its scope, it all has to originate from various sources. This is where the point source and nonpoint source distinctions become important - in describing the source of said pollution. So, without further ado, "point source" refers to a distinct, identifiable source of pollution, and "nonpoint source" designates a pollution source that is not readily identifiable and often pollutes on a large scale, making their pollution difficult to regulate or mitigate. For a few examples, let's consider various aspects of the "typical" lifestyle in the United States. Cars and trucks, for instance are mobile sources of air pollution on a very large scale. Though their emissions are often regulated, it is impossible to reliably enforce certain emissions standards 100% of the time; the combination of these factors suggests that vehicles are, on the whole, a nonpoint source of pollution. The factories that manufactures these vehicles, however, can sometimes be considered point source polluters. In the case of factories who dump their waste onto nearby land, they can be considered point sources of pollution because their pollution can be traced directly back to them and can probably also be regulated. In the case of people's houses, things get a bit more complicated. Gas furnaces, for instances, can be collectively considered a nonpoint source of pollution, even though they are somewhat regulated. However, people who dump toxic chemicals on their lawns are creating point sources of pollution, as these will proceed to run off into the gutter and end up in local water. On the subject of electricity, the power plants that are responsible for the energy used by home appliances can be both point and nonpoint pollution sources. Though the carbon they release as a byproduct of burning coal cannot be accurately traced back to individual plants, certain plants may well be point sources of pollution, depending on whether or not they dump waste into the water supply or damage the land around them (which, hopefully, they do neither).
Based on all of these examples, I hope that the distinctions between these two different types of pollution are more clear. Both kinds of polluters are responsible for a whole slew of pollution, though point sources seem to lean more towards localized environmental effects, such as those of waste dumping, and nonpoint sources bear more responsibility for regional and global pollution, as in the case of carbon emissions.
Hopefully, this small post has helped someone out there become more aware of the various differences, distinctions, and classifications of what has been so broadly called "pollution," and can use this information to some benefit in their own lives and experiences.