Community Cats refers to any cats found outside in your neighborhood, village, town or city. They may be acclimated to humans and may be indoor/outdoor owned pet cats. They may be stray cats who have become lost from their humans or abandoned and may be somewhat fearful. Or they could be "feral" and completely unsocialized when it comes to humans and pretty fearful. Since cats exist on a spectrum of all of these different types, the term feral has somewhat fallen out of social use. You can get more details from some of the links below:
Alley Cat Allies does a lot of great work for community cats but one thing that's particularly cool on their website is their PDF about how to advocate for humane laws and policies for cats in YOUR community! Check it out here