When a fire is barely burning, it's smoldering. Fires can smolder for days without anyone's knowing, then burst into a conflagration that gets the fire department sirens wailing all over town.
Smolder is a word that is often used figuratively to describe situations or people's feelings. You might say tensions between the North and South were smoldering for years before the outbreak of the Civil War, or that the taking away tater tots was like oxygen to the students' smoldering dissatisfaction with food at school.
