A spectrum is a range of different things arranged in order, usually from one extreme to another. The word originally described the rainbow of colors you see when white light passes through a prism: red, orange, yellow, green, blue, indigo, and violet, all flowing smoothly from one to the next. Scientists still use spectrum this way when talking about light waves, radio waves, and other forms of energy.

But the word has expanded beyond physics. When someone says “the political spectrum,” they mean the range from very liberal to very conservative, with many positions in between. A teacher might say students' test scores fell across a wide spectrum, meaning some scored very high, some very low, and many landed somewhere in the middle.

The key idea is that a spectrum doesn't have sharp dividing lines. Colors in a rainbow blend gradually into each other; there's no exact moment when blue becomes green. Similarly, when we talk about a spectrum of opinions or a spectrum of abilities, we recognize that people don't fit into simple categories.

You might hear people say someone is “on the spectrum,” which is shorthand for being on the autism spectrum, a way of describing the range of traits associated with autism. The phrase recognizes that autism affects people differently, and they may need different kinds of support and understanding.