Illustrated Glossary of Organic Chemistry

δ-: A symbol which indicates that an atom or region with an excess of electron density, often because of resonance delocalization, electronegativity differences, or inductive effects.

EN C (2.5) < EN Cl (3.0)
ΔEN = 3.0 - 2.5 = 0.5
Therefore the carbon-chlorine bond of chloromethane is a polar covalent bond.