A bottomless pit is a type of hole in the ground that is infinitely deep. They are so named because they do not have bottoms or floors.
Bottomless pits can be distinguished from normal pits by tossing something into it, and listening for an impact sound. You can also try tossing something living into the pit (such as a person you don't like) and listening to it's terrified screams as it makes it's descent. Assuming these screams trail off into the distance without being interrupted by a horrific "splat", then you've found a genuine bottomless pit.
There is much conjecture as to what happens to things when they fall or are tossed into a bottomless pit.
One hypothesis opens by tentatively suggesting that matter accelerates towards the nonexistent bottom until it reaches a terminal velocity, then continues to fall forever. An interesting side-note to this theory is that matter can easily escape from the gravitational pull, and can be retrieved once it's gone in (unlike a black hole)........... although the time required to retrieve these things increases exponentially the longer it's been in there.
Some arguments against this theory say that all matter would eventually be destroyed due by the bouncification effect (when it inevitably started drifting into the walls).
Common sense dictates that this hypothesis will never gain credibility as a theory since there is no indication that a bottomless pit has to operate in strong gravitational environment.
Or is it?
A second hypothesis - widely thought of as pseudoscience by most academics - argues matter would eventually hit the bottom because there is no such thing as a bottomless pit. These highly controversial theorists point out the fact that all objects in the universe with a ground have a finite size where infinite travel towards the same downward direction would eventually lead to the other side. This has since been dis-proven by Isaac Burke's law of infinite down-ness
A third theory is based on the sound principle of common sense. In this case common sense contradicts pseudo-scientific speculating. Common sense tells us that it is actually very easy to have a bottomless pit.
All that's needed is to dig a pit on one side of the planet, go straight down, and exit at the other side. This type of pit has no bottom.
One investigating committee suggested that the problem could be solved by using space-based cranes to turn the world on it's end and keep it there, but a second committee wisely persuaded them to forget the whole idea.