Simple Explanation of Font Terms Medium, Semi-Bold etc

[saleemus]

Hi there

I have been looking at different font options and i am slightly confused by some of the terms. Can any body tell me where the "Medium" and "Semi-Bold" fonts fall in relation to the terms: Display, Subhead, Body/Text, Caption. I have read the following article: Adobe - Fonts : Type topics: Optical Size but still don't know where they fit in.

Thank you

[MiguelSousa]

Optical Size terms are orthogonal to Weight terms, and thus have no relationship. Think of Optical Size as a different axis, similarly to how the Width axis (Compressed, Condensed, etc) is independent from the Weight axis.

[saleemus]

Thank you Miguel.

So, what would 'Medium' and 'Semi bold conventionally be used for? I'm just trying to figure out if i need to buy them or not.

Best wishes

[MiguelSousa]

That's up to you. There's no prescription to when to use Medium, Semibold, or Bold. Use Medium or Semibold wherever Bold looks too heavy, I guess.