hehehe .. .this is indeed not the easiest thing to explain, but I told the following to my fiance ... hope it helps (no pro's or con's mentioned)!
Jailbreaking the PS3 is the ability to trick the PS3 with a third party device in order to load and run applications that are not approved by $ony.
The third party device (development boards, calculators, iPods, etc) is programmed (on a PC) with a payload that disables certain securities and enables a high level debug mode on the PS3.
This way, two additional menu entries appear under the "Game" option of the XMB which is otherwise hidden from the XMB.
For now, the one option is used to install third party software (homebrew or unsigned code) and the other to run games which is backed-up or copied from an original BD to either an internal or external HDD with the use of third party software - this is currently the most common use for jailbreaking the PS3. There are however devs working on other software (homebrew) not limited to backup managers.