The portable hole is a common magical item in both role-playing games and fantasy fiction (and cartoons as well).
The portable hole is a circle of magic cloth roughly 6 feet across. It is said to be woven from the webs of a magical spider, and infused with the essence of the astral plane. To use a portable hole you simply unfold it, and toss it upon any non-living surface. It will create a hole about ten feet deep. This hole is extra-dimensional in nature, for example, you could toss it onto a table, and a ten foot deep hole would appear on the top of the table, yet it would not penetrate the bottom of the table top.
You can fill a portable hole as full as you would like. Then you simply grab one of the edges, and fold it back up. It becomes no heavier (no matter how much you fill it). You can even store living creatures inside of one of these, except that the hole does not produce its own air, so creatures will suffocate quickly, unless air is somehow provided.
The best use for a portable hole is not as an escape device, it is to carry outrageous amounts of equipment, without worrying about weight or bulk (feel like hauling your entire collection of armor on every mission, no problem).
Portable holes do not mix well with bags of holding (or any other item that produces an extra-dimensional space). Placing one of these items inside the other will destroy both of them (and anything inside), and will probably suck anyone on the vicinity into an alternate dimension.
This is only my interpretation of this item, which is based largely upon its use in the older versions of the Dungeons & Dragons series of games. Your portable hole may vary, so always read the instructions.