Used to describe something that is full to the point of spilling over.
La copa de agua estaba rebosante, y cada vez que alguien se acercaba, el líquido parecía querer desbordarse.
The cup of water was overflowing, and every time someone approached, the liquid seemed ready to spill over.
La caja estaba rebosante de chocolates y caramelos.
The box was overflowing with chocolates and candies.