Definitions for "Low E"
A glazing unit made with either a special coating or in combination with a gas fill (see argon filled) meant to reduce energy transmission through the glazing.
This designates low emissivity glass which means the pane of glass has had a film applied that will block long wave infra red energy, but allow short wave to enter. To read more on Low E.
Glass - Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.