It’s on every ballot. Whether you compete online or in person, it's one of the subtle speaking skills that an untrained listener will intuitively understand without necessarily knowing what to call it. Some speakers are just more pleasant to listen to as they speak, and you can learn to be one of them!
When you hear the term ‘vocal variety’ what do you think it involves?
What kind of variety could you get out of your palette of primary colored paints? Lots, right? How do you get that variety? By mixing in various amounts, obviously! While it may not be quite as intuitive, the same principle applies to your voice and its qualities. You can mix and match these to give a variety of results that make you more auditorily pleasing to your audience. A novice speaker is going to be concerned with writing a speech and memorizing it and getting it delivered. A not-so-novice speaker can begin to deliver it well using more vocal variety.