Trademark...What is it?

Nowadays we regularly see the letters "TM" in text, but what does TM (Trademark) actually mean? A trademark is something that a company/business creates for their products or things associated with their company or products. Trademarking their product means that no other businesses have the right to copy the name/design of their trademark and, if they do the company with the official product have the right to take the other company to court. Some common examples of Trademark being used are with Coke or Diet Coke, these are both products created and owned by the Coca-Cola Company and, because they are Trademarked, the names cannot be copied. Companies can also trademark things such as logos or slogans, for example the Nike tick, or swoosh, is trademarked by Nike meaning that no other companies can copy that logo.
The TM logo isn't actually used that frequently, we normally see the letter R encased in a circle (see below) which means that the product or logo's trademark has been officially registered.