The phrase "central focus" refers to the most important or prominent aspect or subject of something. It is what captures the main attention or spotlight. Full definition
The program's central focus on formative assessment creates opportunities for reflection and feedback tied to the program's content. (learningpolicyinstitute.org)
For instance, one of my clients works in the medical transplant field, and she's writing a thriller whose central focus is about an illegally obtained organ. (thewritelife.com)
Instead, it's a part of our lives, and our relationships should be taking central focus. (juliedillonrd.com)