The complexities of leading / line height / line spacing are much more detailed than this, but I'll write that stuff up separately. For now this image addresses the major point that's been on my mind lately.
"Leading is like jelly betwixt the bread of a typographic sandwich. Line spacing is equal to one layer of jelly plus one slice of bread. If you have a 48 pt line of type with 12 pt leading, your line spacing is 60 pt.
"Note: A majority of digital software erroneously uses leading to refer to what is actually line spacing. The term leading originates from physical letterpress typesetting where metal strips of various thickness are inserted between lines of type."