This is also usually referred to as on-access scanning. This means whenever you interact with a file, your antivirus program will scan it for threats. Interaction with a file includes reading, writing, and modifying a file. So, when you launch a program, it’s going to be scanned. When you download a new document or install a new program onto your computer, your antivirus software will be working hard and checking if those new files are infected with a virus or not. And even when you make changes to that spreadsheet or report you’ve been working on for a while, it’s going to be checked too. All of this happens as you’re using your computer. There’s no need for you to open the antivirus program.
This is when you ask or schedule the antivirus software to scan a specific set of files. It could be when you’re uncertain whether a file is safe or not. Most antivirus programs allow you to right-click the questionable file and ask the program to scan it for threats. You’re also not restricted to a single file. You could even ask your antivirus software to scan your entire hard drive for infections. Usually, that’s not necessary because the software will automatically set up weekly scans for your entire computer.