Baseline: The line where the letters sit.

Cap height: The distance from the baseline to the top of the capital letter.

X-height: Located in between the baseline and the cap height, it's the height of the body of the lowercase letter. 

Bowl: The curved part of the character that encloses the circular or curved parts of some letters, like 'd,' 'b,' 'o,' 'D,' and 'B.' 

Serif: The slight projection finishing off a stroke of a letter in certain typefaces. 

Descender: The longest point on a letter that falls beyond the baseline.

Kerning: the modification of the space between two letters.

Leading: the distance between the baselines