A Be Star is an early star, generally B-type Star, with Emission Lines, generally Hydrogen Balmer Series lines. An A-type Star might be lumped in as a Be star or called an Ae Star. Similar for O-Type Star.
Current theory is that they are rotating rapidly, and heating a Circumstellar Disk of gas ejected by the rotation. Many show overlaid H-alpha Emission and Absorption Lines, each with considerable Line Broadening, the former indicating the rotation of the disk and the latter, the rotation of the star.
A B(e) Star and a Be star are different types, the former being a B-type star with forbidden emission lines.