Last updated: August 15, 2026 · 8 min read What is Sleep? We spend a significant portion of our days and our lives sleeping. It might be the activity that we spend the most time on. But what is it? It is one of those aspects of life that we are so used to that we give little thought to. However, sleep is mentioned as one of the core pillars of a healthy lifestyle alongside other elements such as proper nutrition and exercise.