The cap height is the distance from the top of the capital letter to its bottom. Some vertical elements (ascenders) may extend slightly above the cap height.
The x-height is the height of the main body of the lowercase letter (or the height of a lowercase x ), excluding its ascenders and descenders. The bigger the x-height is in relation to the cap height, the bigger the letters will look.
The baseline is the most stable axis along a line of text. The curves at the bottom of letters such as a or c hang slightly below the baseline. Commas and semicolons also cross the baseline. If a typeface were not positioned this way, it would appear to teeter precariously, lacking a sense of physical grounding.