When I disconnect my cable internet I get
options for wireless.
One is named "Default"
Can someone explain what this is and what are the ramifications of using it?.
Default usually just means the one that is pre-selected (either by you at some earlier point in time, or even by the computer). If you have a wireless network that you haven't named something else, it's probably yours.
No ramifications, except that you may want to secure it with a password and encryption so your neighbors can't use it.