Note that this is a UK/EU perspective and laws do vary across territories.
1. A trade mark is anything that identifies the goods and services of a business or distinguishes them from those of another.
2. A registered trade mark gives statutory protection and an effective monopoly in respect of that mark for the goods or services it is registered for AND for similar marks with the same or similar goods where there is a likelihood of confusion. Well known registered trade marks have additional protection if used by others for different goods or services to those for which they are registered if that use takes unfair advantage of or is detrimental to the repute of the well known registered mark.