Avid Reader

Avid Reader is a Reading perk in Kingdom Come: Deliverance, which can be unlocked at level 7.

Description

Your level of study of the book you've read most of will advance automatically while sleeping or skipping time.

This is quite possibly one of the most under-rated perks in the game, as it allows Henry to improve his stats in his sleep or while waiting (skipping time) as long as he has at least one unread book in his inventory that he has the required skill to read.
Interestingly, this perk is agnostic to other perks and buffs. If Henry has a base Vitality of 13, buffed to 15 by the Resistance perk, he will be able to 'sleep-read' or 'wait-read' Marathon (book) IV due to his overall vitality being 15, but unable to read it while awake due to the base vitality being below 15.
The rate in which a book's Progress fills per hour will increase based on Reading skill for both Sleeping or Waiting. Both Sleeping and Waiting have the same progress rate. This can be viewed in the inventory by highlighting a book and checking the Item Info.
This perk will grant XP at roughly 1/3 the rate of actually Reading the book.
Actual Reading has a daily cap. After it is met, a prompt on screen will state "You can't focus on reading anymore - you've read enough today". However, this perk has no such limit.
The amount of XP gained does not increase. Skill books have preset XP values. You can increase the speed in which you get the XP, but not the total amount.