* Εστίαση (estiasi): This is probably the closest single word and generally translates to "focus" in the sense of concentration or attention. It's often used in the context of focusing one's attention on something.
* Συγκέντρωση (sygkentrosi): This means "concentration" and is a good option when referring to mental focus.
* Επικέντρωση (epikentrosi): This translates to "centering" or "centralization," and is suitable when talking about focusing on a central point or idea.
* Προσοχή (prosochi): This means "attention," and while not a direct translation of "focus," it can be used appropriately depending on the context.
Therefore, the best Greek word for "focus" depends heavily on the specific meaning you intend. Εστίαση (estiasi) is a good general-purpose choice.