Complex sentence: Classical Be stars are B-type stars close to the main sequence where an "e" is added on--hence B (e) star--signifying that Pleione exhibits emission lines in its spectrum rather than absorption lines, which is what stars usually show.
Split into simpler sentences: Classical Be stars are B-type stars close to the main sequence. The "e" in B (e) star means that Pleione exhibits emission lines in its spectrum rather than absorption lines, which is what stars usually show.