Difference between the scans

Can someone please tell me what the difference is between QUICK, STANDARD AND THOROUGH SCANS? Also, what are the ‘Archive’ files it scans if you select that option?

I always tend to do a thorough scan and select to scan Archive files but surely this is not necessary every time?

Justin i can respond only for archive some time there are some virus that is hiding on your archives so Avast will verify if there are some virus on it or not

What is, avast Help file, see image, click to enlarge.