The Book of Skill.
The Book of Skill is an unreadable Tome item in Act II of Diablo II. It can be obtained after defeating Radament for the first time, completing the Radament's Lair quest. Upon 'reading' the Book of Skill the player is rewarded with one Skill Point. Note that the Book of Skill drops only once per Difficulty: you cannot 'farm' Books of Skill by repeatedly killing Radament.
Story Tomes — Moldy Tome • Horazon's Journal
Items — Book of Skill • Lam Esen's Tome • Tome of Town Portal • Tome of Identify