Mono-spaced (or fixed-width) fonts

Mono-spaced fonts such as Courier and Courier New use the same amount of horizontal space (space for the letter plus white space for the background of the letter) for any letter. For example the horizontal space used for the letter "j" is the same as that used by the letter "k".

Example of a mono-spaced font:

Proportionally spaced (or variable width) fonts

Proportionally spaced fonts such as Arial, Times New Roman, Helvetica, Verdana, Georgia and Geneva use a different amount of horizontal space depending on the width of the letter. For example the horizontal space used for the letter "j" is less wide than that used by the letter "k".

Example of a proportionally spaced font: