Typeface is the collection of letters. While every letter is unique, several shapes can be shared across letters. Typeface is the representation of shared patterns throughout the letter collection. These typefaces are chosen as per their legibility, style as well as readability.
Whether you believe it or not, there are certain principles being followed when working on typographic design. One of these aspects would be the baseline. This is actually an invisible line wherein the text rests.
The baseline is also used for measuring:
Now for this one, it basically measures the flat capital letter of typeface that is measured from baseline. Pointed and round capital letters similar to A and S are adjusted optically by drawing it with slightly overshoot above cap height in attaining the effect of having the same size.
Ascenders & Descenders
This is the upward vertical stroke that’s found in several lowercase letters. It extends beyond either the baseline or cap height. Then we also have descenders.
This is practically the downward vertical strokes in letters.
In some instances, there’s a collision between the strokes that may occur when line height is too tight. Then we also have the weight. In essence, this is the thickness of the font.