Different description from the Avast! 5 help file:
avast! antivirus 5.0 contains the following real-time shields:
File system shield - checks any programs at the moment they are started and other files at the moment they are opened or closed. If anything suspicious is detected, the file system shield will prevent the program from being started or the file from being opened to prevent any damage being caused to your computer and data.
Mail shield - checks incoming and outgoing email messages and will stop any messages containing a possible virus infection from being accepted or sent.
Web shield - protects your computer from viruses while using the internet (browsing, downloading files etc). It will detect and block known or potential threats coming from the web e.g. hacked web pages infected with (potential or actual) malicious scripts. If a virus is detected while downloading a file from the internet, the download will be stopped to prevent the infection from reaching your computer.
P2P shield - checks files downloaded using common peer-to-peer (file sharing) programs.
IM shield - checks files downloaded by instant messaging or "chat" programs.
Network shield - monitors all network activity and blocks any threats that are detected on the network. It also blocks access to known malicious websites based on the avast! database of infected URLs.
Script shield - only in avast! Pro antivirus and avast! Internet Security. This detects malicious scripts and prevents them from being run. The script shield will detect and block not only malicious scripts coming from the web (remote threats) but also scripts coming from other sources, such as web pages saved to disk or in the browser cache etc (local threats).
Behavior shield - monitors all activity on your computer and detects and blocks any unusual activity that might indicate the presence of malware. It does this by continuously monitoring your computer's entry points using special sensors to identify anything suspicious.
