What is the difference between Fresh Air Supply, and Fresh Air Machine?

The difference between the two is small, but your use case may vary. See below for more details on Air King Fresh Air units. 

Fresh Air Machine: Generally utilizes air coming directly from outside and is not conditioned. Contractors and builders now have a practical offering for introducing constant fresh air from outside into the residence, meeting the fresh air CFM requirements for ASHRAE 62.2. Inexpensive first cost method to bring in fresh air using an independent fan

Fresh Air Supply: More likely to be used with air that has been fully conditioned (cooling or heating). It is designed for use with a smart thermostat (purchase separately). The fan is nearly silent Energy efficient 120V motor results in low operating cost and can operate independently of air conditioning and heating units. Programmable to prevent temperature & humidity extremes