What is the key difference between the term "Research Gaps" and the terms "Literature Survey" or "Literature Review"?
The difference between "Literature review" and "Literature survey" is small, if it exists at all - people may use the two terms to mean the same thing. It has been discussed in this question.

A "research gap" is an area of research that has not yet been done. You may identify a research gap by doing a literature review or survey.