Not what IS jailbreaking, What does Jailbreaking do to the iphone?

[timcki]

I know how to jailbreak, install apps, etc. but , what does it change in the phone ??

does it change the files system to be writeable?

sorry if this is too vague of a question, curiosity finally got the best of me.

[mrrippey]

makes the file system read/write