Catalina is the latest macOS version (macOS version 10.15). It was released on Monday 7 October 2019; you can find out more about Catalina on Wikipedia.
Catalina brings a number of important technical changes to the Mac platform, for example, Catalina has a read-only root file system, but we don't know yet if or how this will impact Daedalus. It also prevents 32-bit applications from running so is likely going to orphan older software but not Daedalus.
Generally, Daedalus should be compatible with Catalina but we have not tested it yet so we do not know what the impacts of running Daedalus on Catalina are.
We do know that you will face this known issue Installation of Daedalus on Catalina blocked (macOS) if trying to upgrade to Daedalus 0.14.0 AFTER updating to Catalina. (If you have the latest version of Daedalus installed on your Mac and then update to Catalina and then try to run Daedalus you should be OK).
We will update this page with any further information on issues related to Catalina as we become aware of them.