Fundamentals are something you can break down universally and apply it to every fighting game without prior knowledge of the title.
fundamentals in fighting games means you fully understand the concept of footsies (and i dont mean just saying the word to sound cool, i mean actually understanding), spacing, whiffing and punishing. These are 4 basic mechanics that exist in every fighting game and it can take you a long way.
Also, fundamentals =\= skill whatsoever. Having skill at one game does not mean you are fundamentally sound with fighting games. It takes years of experience to truely understand the intricacies of fighting games and their mechanics.
The best example of fundamentals in a person would be Justin Wong. He truly understands what fighting games are about. When it comes to Justin, hand him ANY game and in less than a month, maybe even a week, he can compete with anyone on the planet.
Now I see some people said execution is a big factor.. yes and no. It's good to have basic execution, understanding motions and executing them at will without any thought, but thats as far as it goes. In a game like street fighter, its possible to win with ANY character without landing so much as a 2 hit combo, as long as you are "fundamentally" sound and understand what situations you get into. Learning basic combos will get you far, it never has to be fancy or optimized.
Hope this helps @
FOREVER EL1TE