To scan means to look over something quickly to get a general sense of it or to find something specific. When you scan a page in a book, you're not reading every word carefully. Instead, your eyes move rapidly across the text, picking out key words or searching for a particular name or fact. Students often scan their notes before a test to refresh their memory, or scan a menu to find their favorite dish.

The word also means to examine something systematically and thoroughly, which seems like the opposite but really isn't. A doctor might scan a patient's body using special equipment that creates detailed images of what's inside. Airport security scanners examine luggage piece by piece. A ship's radar scans the horizon, sweeping back and forth to detect other vessels. In this sense, scanning means checking everything carefully and in order, like how your eyes scan across each line when you actually read instead of just glancing.

You can use scan as a noun too: “The MRI scan showed a broken bone” or “A quick scan of the room revealed no empty seats.”

The key to understanding scan is recognizing that whether you're scanning quickly or thoroughly, you're always searching or examining systematically rather than randomly.