The Japanese dictionary simply defines it as one who was born and raised in Edo or Tokyo.
However, popular definitions of "a true Edokko" include the following: The latter case is rare in reality, as the majority of the Edo/Tokyo population consists of the natives of other areas.
Historically, Edokko almost exclusively refers to chōnin, the commoners.
The majority of samurai in Edo were from the countryside, and Edokko satisfied themselves by looking down on them, referring them being yabo, the opposite of iki.
[1] From this form is also derived the word edochiano, the Italian-language demonym for people from Tokyo.