This is Dream Theater's eigth studio album. This album is notable special because it was the last album ever recorded at The Hit Factory in NYC (the first being Stevie Wonder's Songs In The Key Of Life).
Dream Theater has not specifically given information on what the title of this album refers to. Some fans believe that it refers to the Octavarium, a book of Catholic liturgy about a period known as the Octave. Others believe that it is simply referring to the number eight, and some think it alludes to musical octaves. Unrelated, it continues a pattern started with Dream Theater's Six Degrees of Inner Turbulence, which was their sixth studio album and had six songs. Train of Thought was DT's seventh album and has seven songs, and Octavarium is DT's eighth album and has eight songs.