Ultra- is a prefix that means “beyond,” “extremely,” or “to an excessive degree.” When you add ultra- to the front of a word, you're cranking up the intensity to a very high level.

An ultramarathon is a race longer than a regular marathon, often 50 or 100 miles. Ultrasound uses sound waves beyond what human ears can detect. Something ultramodern pushes into cutting-edge territory, going beyond what's merely modern. When scientists study ultraviolet light, they're studying light rays beyond the violet end of the spectrum that our eyes can see.

In English, we use it to signal that something has gone past normal limits. An ultra-thin laptop is thinner than thin. Ultrasonic frequencies are sound waves pitched higher than humans can hear.

Think of ultra- as the word-building equivalent of turning the volume knob way up. It takes whatever follows it and pushes it into extreme territory.