Here is a paragraph of text with normal line height. Line height is the vertical distance between the baseline of one line of type and the next. This distance is a proportion of the font-size. For example, if the font-size is 12 pixels and the line-height is 1.5, then the distance between the lines is 18 pixels.

The default line spacing is typically 1.2, but this paragraph has a tighter setting of .8, meaning the descenders of one line will touch the ascenders of the one below if they appear above one another.

This paragraph has a looser setting of 1.5. Now the line spacing is 50 percent greater than the font-size. This a nice way to give an elegant look to your typography, but is a less efficient use of the vertical space.