Is the infinity symbol a number?

In math, infinity is defined as a number larger than you are able to measure. So if your ruler is 12 inches, 13 inches is a infinity*. Many people never learn that definition, so they assume that infinity means "without limit". So many people believe that that you just have to accept it as common knowledge. So one way it's a number, the other way it's not.

*The longest ruler we have is the width of the Earth's orbit. By measuring the angle to a star we can reliably calculate distances to about 3200 light-years. Beyond that is infinity. That is why estimates of sizes beyond 3200 light years have such large error margins. Some people think they can measure distances farther than that. Those estimates are based on guesses and assumptions.