Bug vs Defect vs Issue

I saw this as a ym status of a colleague who is a QA and since I'm also doing QA works now, I wondered myself what's the difference. And here's what I found:

Bug
- things that a software does that it's not supposed to do
- things that a software doesn't do but it's supposed to do


Defect
- a quality problem that is discovered after the program has been deployed to clients

Issue
- can be a bug or a feature enhancement request


Reference: http://testdog.com/knowhow/bugs vs defects.html