The Telestial Kingdom is the lowest of the three "degrees of glory," in which the highest or Celestial Kingdom is compared to the sun, the middle or Terrestrial Kingdom is compared to the moon, and the lowest or Telestial Kingdom is compared to the stars. Also, "in addition to the degrees of glory, there is a place of no glory, called perdition, reserved for those who commit the unpardonable sin." (Bible Dictionary: Degrees of Glory)
Persons who will attain the Telestial Kingdom in the afterlife, according to the Church's teachings, include those "who received not the gospel of Christ, nor the testimony of Jesus" (Doctrine and Covenants 76:82) as well as "liars, and sorcerors, and adulterers, and whoremongers, and whosoever loves and makes a lie" (Doctrine and Covenants 76:103). These people will suffer in hell before reaching the Telestial Kingdom, however the Telestial Kingdom is not unpleasant: "the glory of the telestial...surpasses all understanding" (Doctrine and Covenants 76:89).