Communicating online means transferring data from one person to another or a group of people. This is often done through social media and specialist software.
A online community is a virtual community (a group of people) which only exists online. It is also known as a network of friends. Example: YouTube, Macmillan Cancer Research.
A virtual world is a unreal world created online for people to create characters and be them. One of the most famous ones is World Of Warcraft where people are also able to play with people all over the world.
Communicating online requires people to behave a certain way. If rules are broken then people are often stopped from communicating for a certain amount of day or permanently blocked from communicating. You can also be reported by other users if rules are broken.