First of all, what is 'HTTP'? HTTP is an acronym for "Hypertext Transfer Protocol". Its main use is to tranfer "hypertext" information, such as webpages (including images etc.). For example, viewing the website http://www.peerblock.com transfers the webpage via HTTP.
HTTP typically uses port 80 to transfer information, or port 443 to transfer encrypted ("HTTPS") information, such as credit card transactions on e-commerce websites. HTTP can however be used on any port. Port 80 and 443 however can be used to transfer any infomation - it does not need to be HTTP.
By default, PeerBlock blocks all connections on your blocklists over any port (including 80 and 443). You can choose to "Allow HTTP", which will allow any connections on both ports 80 and 443, including traffic that is not HTTP, because it travels on the ports typically used for HTTP.
What does this mean? It means that if you allow HTTP you leave a possible hole in your protection. If you block HTTP, you may not be able to view some websites that's IP Adresses are on your blocklists.
It is recommended to keep HTTP blocked, and to allow individual IP's for websites you would like to view. If you would like to do this, see Allow Lists.
If you would like to know whether HTTP is blocked or allowed for you, it is shown in the following location:
Click to see full size
Note that HTTP blocks are listed in the Log Window are show (by default) in blue. This color can be changed in Settings