Cronenberg World is Earth in a dimension where people on Earth are naturally Cronenbergs. The Rick and Morty of this dimension leave after they accidentally turn the entire world into regular Humans. They take a portal to Earth (Dimension C-137) when they discover that C-137 Rick turned almost the entire population of Earth (Dimension C-137) into Cronenbergs in the episode "Rick Potion No. 9".
The word "Cronenberg" is a reference to the Canadian filmmaker David Paul Cronenberg. Which, according to Wikipedia: "He is one of the principal originators of what is commonly known as the body horror or venereal horror genre. This style of filmmaking explores people's fears of bodily transformation and infection."
“Here we are Cronenberg Morty, a reality where everyone in the world got genetically Cronenberged. We'll fit right in Cronenberg Morty. It will be like we never even left Cronenberg World.”
“I'm going to ya know miss Cronenberg world because everyone was Cronenberged all along like us from the beginning ya know. I mean I wish we hadn't genetically ruined Cronenberg World beyond repair like we did ya know and turned everyone into regular normal people.”
It's implied that the Cronenberg World's Cronenbergs are fully capable to speech and thinking. This differentiates Cronenberg Rick and Morty from other Cronenbergs of Earth C-137 as they can fully think and talk like normal people.