Colonialism is the expansion of a nation's sovereignty beyond its borders through the establishment of colonies. It is usually seen as a substantial part of imperialism, especially when involving sovereignty over foreign cultures or peoples. The word today is usually tied to the European expansion during and after the Age of Exploration and involved lands that were far away from the nation ruling them.
Colonialism typically involves the spread of a nation or people's culture through the establishment of new settlements (e.g. English settlement of the New England states) or population transfers to existing settlements (e.g. Dutch dominance of South Africa.)
Misuse of the Term
Anti-American sentiment and liberals in general commonly deride American foreign policy as colonial or imperial, which is deceitful, as the United States has no colonies (having relinquished the Philippines, which had previously been Spanish, not sovereign), made Hawaii a state, smaller lands (Guam, etc...) protectorates, and purchased or legally acquired other territories (Guantanamo, Panama Canal). Similarly, liberals also generally imply with colonialism that it was generally parasitic to the original people and stealing resources, when that is actually rare among colonialization.
There are many common myths and misconceptions associated with the term. Texts generally claim European peoples established foreign colonies because of "overcrowding," and imposed their administrative laws on native people's. In reality, colonialism was an expansion of trade opportunities intended to develop markets for European manufactured goods. Colonies were typically established among tribal people who were often dominated by warlords, where laws varied in the same region from tribe to tribe. Natives often welcomed European administration and courts, which brought a more uniform system of justice and more prosperity for the surrounding region.
South Africa is a prime example. During the Apartheid period it was said South Africa's native blacks were an oppressed majority. South Africa's majority blacks are not native to South Africa - they are the descendents of economic migrants who came to South Africa to participate in the economic development that white Europeans brought to South Africa. Whites also brought a more just administration of laws than migratory blacks found among their native tribes and regions.
During the Cold War, South Africa was a ripe target for Kremlin-directed Marxist propaganda. Soviet financed Marxist hate speech and lies live on in the Social Justice Warriors who rule South Africa today, driven by racial animus, political correctness and a hatred for freedom, capitalism and Western Civilization.
India is a massive subcontinent that willingly embraced British administration and laws to govern the myriad of commercial disputes that inevitably arise from economic development. India's hundreds of tribes and languages were ill-situated and ill-equiped in a domestic environment that had been feuding among itself for nearly a millenium, often violently, whether to live under Sharia law administered by its Muslim minority, of some other localized system. The white Europeans brought with them a system of laws that seemed more democratic, along with job opportunities, prosperity, and trade that hadn't previously existed.
It was the anti-capitalist leftists of the Cold War, like Russbots repeating Kremlin directed talking points, that have dominated the Western educational system and have driven the planet toward global race war on false premises.
Yemen is a great example of the tribalism, chaos, and warlords who dominated and controlled the region, and still do. Colonial rule never extended outside the port of Aden, which the British Empire deemed a necessary beach head in the pirate infested waters between Suez and Bombay. The waters are still some of the most dangerous and lawless pirate infested waters on the planet, and are a constant threat to global shipping and trade.
Beirut and Lebanon
Beirut is a French colonial port city the French Empire had carved out for itself for off-loading and sale to the Arab world of French manufactured goods. Because French exporters and traders, and the French government, could never come to terms with locals who wanted to use Shariah law to settle commercial disputes (Shariah law has no areas governing corporations), France carved out for itself the province of Lebanon staffed by a local, secular Arab civil service.
France never had control of Syria, Lebanon, or Beirut as the anti-colonial Marxists' and communists present in American universities and textbooks. France was always dependent on secular locals who willingly volunteered to cooperate with France, and occupied all the positions of the Western-style civil service. These native Arab collaborators viewed the teachers and enforcers of Shariah law as their oppressors.
Indeed, the modern nation state of Syria was created in a non-competition clause of a trade agreement between the British and French Empires. Syria would not exist as a bureaucracy or state entity otherwise (recall, Shariah law does not recognize corporate entities, and secular governments are corporate entities) and was always staffed by secular locals who respected the rights of foreigners and non-Muslims.
This confusion of facts in Marxist propaganda and American school textbooks has led to some amazing, outlandish, and incredible dichotomies and claims. In 2014 for example when the Islamic State was declared, Wikipedia claimed that Syria had won its "independence" from France in 1940 when France "liberated" Syria from France. The article has since been cleaned up somewhat, but still leaves more questions than answers for serious students seeking to understand the contemporary Syrian conflict, sans Marxist distortion of terms and historical meaning.
Hong Kong is among the most successful "victims" of Western colonialism who have built a native tradition of love for freedom, and whose native population has "suffered and been victimized" by Western prosperity "forced" on the population.