What is the difference between Qiyam al-Layl and Tahajjud, and what is the reward for one who prays them both?

Qiyam al-Layl (standing at night) is broader and more comprehensive than Tahajjud; it is spending the night or part of it in acts of worship such as prayer, reciting the Qur'an, and remembrance of God, and it includes praying before and after sleep. Tahajjud, however, is specifically for prayer, and there are two differing opinions regarding it: one is that it is any night prayer, and the other is that it is prayer performed after having slept. Tarawih is Qiyam al-Layl in Ramadan, performed at the beginning of the night with lightness, and it can be called Tahajjud or Qiyam al-Layl.