The English language is a curious beast, add to that the vernacular used by computer people and you get confused very quickly. In the real world away from computers, the word "default" has connotations of unpaid bank loans and other things with failure of duty - nothing particularly good.
In a weird sort of way, computer people co-opted the term to indicate what happens when you "fail to choose an option". Said in another way, "the default option is that one that happens if you don't select one".
Imagine that your computer is asking you a question: "Are you sure that you want to remove all the files from your computer?" and the answers you can give are "Yes" and "No".
If you just hit the "Enter-key" on the keyboard, the computer would need to choose a "default", that is, figure out what the best response would be if you just banged the key. In this case "No" would be a solid choice and it would be likely outlined with a thicker border around the button on the screen. It's the default answer for this question.
Of course if the question was: "Do you want to save this file before you quit? (Yes) or (No)", the default would be Yes.
Next time you see "default" on your computer, you'll know it's not talking about bank loans or anything "bad".