A free good and an economic good

A free good does exist in such a natural abundance that one's desire can be satisfied at zero price. At zero price, one can get as much commodity as one wants for example, fresh air in LDCs. The cost of acquiring it is zero. It is a good for which demand is less than supply at zero price.

An economic good
arises out of scarcity and choice. It must satisfy three conditions: provide satisfaction (utility); be relatively scarce, and marketable i.e. it must have value.