A Be Star is an early star, generally B-Type Star (B), with Emission Lines, generally Hydrogen (H) Balmer Series lines. An A-Type Star (A) might be lumped in as a Be star or called an Ae Star. Similar for O-Type Star (O).
Current theory is that they are rotating rapidly, and heating a Circumstellar Disk of gas ejected by the rotation. Many show overlaid H-alpha (Ha) 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.