To call on someone means to ask them to speak, answer, or participate. When a teacher calls on you in class, she's choosing you to answer a question or share your thoughts. Your hand might be raised, or she might surprise you by calling on you when you weren't expecting it.

The phrase works in other situations too. A coach might call on a specific player to take a crucial shot. During a meeting, a leader might call on different people to give their opinions. When you call on someone, you're giving them the floor and inviting them to contribute.

The phrase can also mean to visit someone, especially in a formal or purposeful way. A doctor might call on patients at their homes, or neighbors might call on each other to borrow tools or share news. This usage is less common today but still appears in older books and formal contexts.

Sometimes people call on someone for help or support, meaning they turn to that person in a time of need. You might call on a friend when you need advice, or a community might call on its leaders during a crisis. In this sense, calling on someone means relying on their strength, knowledge, or assistance.