Illustrated Glossary of Organic Chemistry

Electron donating group (EDG; electron releasing group; ERG): An atom or group that release electron density to neighboring atoms from itself, usually by resonance or inductive effects.

Methyl carbocation Less stable		Tert-butyl carbocation More stable

The tert-butyl carbocation is more stable than the methyl carbocation because methyl groups release electron density via inductive effects or hyperconjugation. A methyl group is an electron donor.

Carbocation without resonance Less stable		Carbocation with resonance More stable

The carbocation with an oxonium ion resonance contributor is more stable than one without because the oxygen lone pairs are shared via resonance. This hydroxyl group is an electron donating group.