The word "rampant" describes something that is widespread, unchecked, or out of control. It often refers to growth or activity that occurs aggressively and without restraint. For instance, you might say that weeds are rampant in a garden, meaning that they are growing abundantly and taking over the space.
The word "rampant" comes from the Middle French word "rampant," which is the present participle of "ramper," meaning "to climb." It was initially used to describe a lion standing on its hind legs in heraldry, symbolizing strength and ferocity, before broadening its meaning to indicate something that is growing or spreading widely.