To inundate means to quickly fill up or overwhelm, just like a flood. Your bathroom could be inundated with water if the pipes burst, and hopefully your inbox is inundated with nice emails on your birthday.
Commonly used to refer to a deluge of water, inundate can also refer to an overflow of something less tangible, like information. Right before the holidays, toy stores are often inundated with eager parents scrambling to get the latest action figures and video games. Attempt to read the entire dictionary in one sitting and you'll inundate your mind with vocabulary. But you probably won't remember any of it tomorrow.