If a system is hierarchical, it is built in levels. Some people or things sit above others: they have more power, more rank, or more importance. A company with a boss, then managers, then workers is hierarchical. Armies, schools, churches, and governments often work this way too. You will meet this word in more formal talk — offices, textbooks, news about organisations — not much in the playground. Though actually, people also use it for things that are not people: a hierarchical list of folders on a computer, or animals in a group with a top animal. The tidy idea is neat levels; real life is messier, and people still call a company hierarchical even when the levels are not as clear as the chart says.