Answer:
Understatement
Explanation:
It is a figure of speech, that means, it is a phrase or word that has other meanings that it's literal one. This is employed to create a vivid rethorical effect. The understatement intentionally makes a situation seem less important than it usually is. An importan fact is therefore shown as something trivial. In has an ironical effect.
It's contrary is the hyperbole which tries to make trivial things look huge or very important.
