natomy of a typeface

Base line: the imaginary line upon which all type rests
x-height: the main part of the lower case which is equal to the height of the lowercase ‘x’
Ascender: the part of the letter form of the lower case which rises above the x-height as in ‘b’, ‘d’, ‘f’, ‘h’, ‘k’ or ‘l’
Descender: the part of the letter ‘g’, ‘j’, ‘p’, ‘q’ and ‘y’ that extends below the baseline

Cap height: height of the capital letter. The ascenders of some lowercase actually rises sometimes a little bit above the cap height.
Type size: refers to the overall depth of the typeface and is measured from the top of the highest character to the foot of the lowest.

Serif: a short stroke that projects from the ends of the character. The serifs help to keep letters a certain distance apart, they link letters together to form word which helps reading and finally they help to differenciate individual letters.
Stroke or stem: vertical or oblique part of a letter. It can be more or less thick or thin.
Counter: An enclosed or partially enclosed portion of a type character such as ‘p’, ‘q’ or ‘b’