What's the difference between i.e. and e.g.?
word-forming element meaning "a speaking, discourse, treatise, doctrine, theory, science," from Greek -logia (often via French -logie or Medieval Latin -logia), from root of legein "to speak;" thus, "the character or deportment of one who speaks or treats of (a certain subject);" see lecture (n.).
Science; theory; study: dermatology.