A single-minded agent is like a robot that has only one goal and nothing else matters to it. For example, imagine a robot whose only purpose is to clean your room. It doesn't care about anything else, like playing or eating or watching TV. All it cares about is cleaning your room. It will keep cleaning until it's done, no matter what happens around it.
Similarly, a single-minded agent is a computer program that is designed to do only one thing, and it will keep doing that thing until it's done, no matter what. It doesn't care about anything else, like other tasks that need to be done or other goals that need to be achieved. It will keep working on that one task until it's complete, even if something more important comes along.
This type of agent is very useful in situations where we need something done quickly and efficiently, without any distractions. But it can also be a problem if we need to be flexible and adaptable, because a single-minded agent can't change its goal or do anything else until it's finished with its current task.