"Clear mucus" refers to a substance that is produced by our bodies, typically in areas such as the nose or throat. It is called "clear" because it is transparent and not colored. Full definition
In addition, keep in mind that coughing clears mucus from the lower part of the respiratory tract, and ordinarily there's no reason to suppress it. (healthychildren.org)
It also opens the respiratory passages and helps clear the mucus associated with a heavy chest cold. (mindbodygreen.com)
If your child has a cold, she might have a runny nose with clear mucus that may thicken and turn gray or yellow or green over the next week or so. (babycenter.com)