Phlegm/flem/ Definition 1 of 2Pro Tip 1/3Illness Related Phlegm usually relates to being unwell, often accompanying a cough or cold. She felt ill and noticed more phlegm than usual. Pro Tip 2/3Viscosity It's a thick, sticky substance, unlike the more watery mucus when not sick. The phlegm was thick and made his throat feel clogged. Pro Tip 3/3Negative Connotation Discussion of phlegm may be considered unpleasant or impolite in some situations. Please don’t talk about your phlegm at the dinner table!