What
How did you first think of the word focus... as a noun... as a verb... as an adjective?

Huh?

Indulge me here for a minute, please – the English teacher in me from eons ago is resurfacing briefly... and it’s for a reason which will come clear a little later.

What something is, that’s the “what”, the definition.

Let’s use this one for focus:

“A concentration of attention” as in… “I believe I can bring you the high degree of focus needed for this job”.

Or…
In focus - in highlight, in a spotlight as in…”The sports budget will be in focus at tonight’s meeting”.

Consider that “focus” used as a noun is out there somewhere, but it’s not yours.