The word tick has several meanings:

1. A small mark used to show that something is correct, complete, or has been checked. In many countries, people use a tick (✓) the same way Americans use a checkmark. When your teacher reviews your homework, she might put a tick next to each correct answer. British English speakers often say “tick the box” where Americans say “check the box.”
2. A tiny spider-like creature that attaches to animals and people to feed on blood. Ticks are parasites about the size of a sesame seed that live in tall grass and woods. They're important to watch for after hiking because some ticks carry diseases. If you find a tick attached to your skin, it needs to be removed carefully with tweezers.
3. A quick, light sound that repeats regularly. A clock makes a ticking sound as its second hand moves: tick, tick, tick. You might hear your watch ticking in a quiet room. People sometimes say something is ticking in movies, referring to this steady sound counting down.
4. What makes someone behave the way they do. When you wonder what makes a person tick, you're curious about their motivations and personality. Understanding what makes your best friend tick helps you know why they love certain activities or react certain ways to situations.