From Dictionary.com
smart
1. a. Characterized by sharp quick thought; bright. See Synonyms at intelligent.
b. Amusingly clever; witty: a smart quip; a lively, smart conversation.
c. Impertinent; insolent: That's enough of your smart talk.
2. Energetic or quick in movement: a smart pace.
3. Canny and shrewd in dealings with others: a smart negotiator.
4. Fashionable; elegant: a smart suit; a smart restaurant; the smart set. See Synonyms at fashionable.
5.
a. Of, relating to, or being a highly automated device, especially one that imitates human intelligence: smart missiles.
b. Manufactured to regulate the amount of light transmitted in response to varying light conditions or to an electronic sensor or control unit: smart windows.
6. New England & Southern U.S. Accomplished; talented: He's a right smart ball player.
The answer to your question is the above definiton (perhaps only 1. and 3. when used in this context) of smart, as I see it best fits if someone described as smart has the properties that are defined by the word "smart".
Why do you want us to define the adjective "smart"? It is already defined in various dictionaries.