You block out the afternoon to finish something hard. You open the document, a message pings, you check it, then another arrives. Three hours later the document looks the same and you can't say where the time went.
Deep Work is a focus practice that has you do cognitively demanding tasks in long, uninterrupted stretches with no distractions. Cognitively demanding means work that needs your full concentration to do well: writing, studying, planning, or solving a hard problem. You protect a block of time, remove every interruption, and give one difficult task your complete attention until the block ends. The term comes from Cal Newport, who named the practice in his book Deep Work.
The opposite is shallow work: the easy, fragmented tasks like email and quick replies that fill a day without producing much. Concentration produces real progress on hard things, and constant switching between tasks destroys it, because each interruption leaves a residue that takes minutes to clear before your mind is fully back. A single protected block gives your attention time to settle and reach the depth where good work actually happens.
Run your hardest task through five steps. Start small and build the habit before you stretch the blocks longer.
You give yourself a 90-minute block on Sunday morning to prepare for a language exam. You put your phone in a drawer in another room, close every tab except the one you need, and ask your housemate not to interrupt you until lunch. For the full 90 minutes you work through grammar drills and write practice sentences, and when your attention drifts toward lunch you note the thought and return to the page.
By the end of the block you've covered more ground than a whole week of scattered ten-minute sessions, because nothing pulled you out mid-thought and your mind reached a depth those short sessions never allowed. You stop, eat, and leave the rest of the day light. The progress came from the unbroken stretch, not from extra hours.