When Avast detects a virus, it usually recommends me to “move to chest”. What does this do?
I don’t understand all the technical ramifications, but the virus chest in Avast! is a “safe holding” area, similar to “quarantine” in some other AV applications like Norton and McAfee. It keeps an infected or suspect file from interacting with the rest of your computer environment/operating system until you have more information as to what exactly it is (i.e. if its something detected during a systemwide scheduled scan, it could be something important, for example) and therefore whether it should be cleaned, restored from a backup or merely deleted.
Hope this helps. 
Churchmouse
To view content, start avast! and choose “Quarantine zone” in the Tools menu.
Yes, avast itself calls it “Quarantine zone” in most places.
(namings should be unified)
The English version of avast! calls it the Chest or Virus Chest, everywhere. Some translators may have decided to translate it otherwise (e.g. as Quarantine) in non-English versions of avast!.
Ok, I will use english version to avoid further confusion.
Igor, I confirm. No problems of homogeneity into English version.
In Portuguese (Brasil), in fact, Chest was translated into Quarentena (similar to Quarentine).
Finaldeathh, do you need more help?