I was doing some practice problems on Linked Lists and I saw this question: "Which of the following doesnotsatisfy the loop invariant for the while loop?"

My question is, what does invariant mean? I know it means constant in English, but what does it mean in math/computer science? I googled it and all this crap about predicate in mathematics came up. Wikipedia isn't really noob-friendly so I thought I post it here. Any help is appreciated and thanks in advance!

P.S. Let me know if posting the whole question will be beneficial.