Proportional
Also called: variable-width
A proportional font is one in which the typesetting width occupied by the letters and other characters depends on the width of the letter itself. In proportional fonts, an m will take up more width than a j. This is in contrast to monospace fonts. The majority of all fonts are proportional.
The advantage of proportional over monospace is that there is always about the same amount of space between letters. Most people find this more pleasant to read. In a non-proportional font, an m and a w will be closer together than an i and a j.
In graphic design and text formatting, proportional fonts can sometimes present a challenge. If a sentence contains relatively many "wide" letters, fewer letters and words will fit on one line and page than if, on the contrary, they are relatively few.