What it is: This is the policy and practice of extending (often with the use of armed force) a government's power and rule into lands and states outside its country's boundaries - sometimes a great distance from them. It is also called expansionism or imperialism.
What it means: There have been many empires in world history, all created by invading and seizing other people's territory. The British Empire was one of the largest in history. At its height it included many colonies, mainly in Africa and Asia. Empire-builders select places for colonisation for many reasons - such as because they were easy to seize, or because their locations were of political importance to the coloniser, or because they contained valuable minerals and other natural products (not to mention cheap labour to process them). Many people from colonising countries went out to live and make money in the colonies, often depriving or exploiting the local population. During the 20th century many colonies became independent, some after fighting wars to do it. But their suffering didn't end there: after years of enforced dependency the people have found it difficult to set up their own governments and other administrative organisations, and in some colonies there have been civil wars between rival groups fighting for leadership. Another way to gain power over other countries is to get control of their trade in goods or raw materials; and many developing countries owe money loaned to them by larger ones and are in their power as a result. Such power is called neocolonialism.
Think about it: Be under no illusions: whatever colonisers may say, colonies are seized for the benefit of the coloniser, not the colonised. Even when colonised people haven't been harshly treated, they have still had a new way of life imposed on them, and many have been forced to be the servants, sometimes even the slaves, of their imperial overlords. (It's not all that long ago that they were disrespectfully referred to as 'natives'.) Their languages and cultures and customs have been treated with disrespect, if only by being thought unimportant or 'uncivilised'. The first colonists in the days of empire-building included traders, there to take the country's produce away (sometimes in return for guns) to sell for their own profit, and missionaries, there to teach the people the coloniser's language and tell them that their religions were wrong. In short, colonising has been one of the most effective ways of creating misery, resentment, and future rebellion, usually armed. Former colonies are still suffering from the effects of being treated as other people's possessions. Colonisation still takes place in non-political ways: think of trade and take-overs. Are there other examples in everyday life?