Management likes to use the word focus. They like it so much, that anything important is called a focus.

That’s an interesting scenario, one which we hope to address, but it’s not our main focus.

We’re focusing on three features for this release.

But how can you focus on more than one thing? The first citation implies that there’s more than one focus (a main focus, and maybe some secondary foci); the second citation makes explicit the mutiplicity of foci. But a lens doesn’t focus on more than one thing. There is one focus, the point at which parallel rays from infinity converge.

Then again, if a lens is defective, it can have more than one focal point. And there’s a term for that phenomenon: Aberration.