According to Dictionary.com pervious is an adjective meaning "open to passage or entrance; permeable". So basically pervious concrete is concrete that is designed to allow rain water to pass through it rather than retain it.

Think about a conventional parking lot during a rain, the water usually runs to a drain and then to some form of storm water management system, frequently a "pond" somewhere on the property. This stormwater management system then eventually dumps into a stream, lake, or other natural body of water. This can be very bad, because this "run-off" water tends to concentrate pollutants and they flow with the stormwater all the way to the stream, lake, or other body of water - eventually causing real environmental damage.

Now think about a pervious concrete parking lot during a rain. The water flows through the concrete into the aggregate base where it can filter down into the earth - just like it did before the parking lot was installed! This reduces pollution by natural filtration and microbial conversion of hydrocarbons. According to the Environmental Protection Agency (EPA) pervious concrete is an important element to consider when designing and/or installing paving. This is also called sustainable development.

Concrete Construction is a good magazine that not only offers great articles about pervious concrete but is a great magazine for anyone involved in the construction industry.