To think means to use your mind to form ideas, make decisions, solve problems, or understand things. When you think, you're working with information inside your head: remembering facts, imagining possibilities, reasoning through choices, or figuring out how something works.

Thinking takes many forms. You might think about what to have for lunch, think through a tricky math problem, or think up a story to write. Scientists think carefully about their experiments. Chess players think several moves ahead. When your teacher asks “What do you think?” she wants to know your opinion or reasoning.

The word also describes believing or supposing something. You might say “I think it's going to rain” when you notice dark clouds, or “I think that's the right answer” when you're fairly confident but not completely certain.

As a noun, a think is a careful period of thinking. You might say, “Let me have a think,” before you answer.

Thinking is what separates a wild guess from a reasoned conclusion. When you think something through carefully, you consider different angles, test your ideas, and use logic. Quick thinking happens fast, like when you catch something before it falls. Deep thinking takes time and concentration, like when you're pondering a really interesting question. Either way, thinking is how you make sense of the world and decide what to do next.