It is used to refer to someone who is constantly changing their mind about something.

I got the impression that the term originally came from fish, when out of water, who flip and flop around trying to get back into the water. The flipping and flopping motion the was used to describe a state of mind - not being able to make up one's mind.

It was just an impression, so I may be incorrect, but still an interesting theory.

To flip-flop means to change one's opinion or position from one side to the opposing side or argument. It has a negative connotation (not a compliment) and there is an implication that the change of position was more impulsive than properly thought through.

In the US, it is an expression that is used almost exclusively in politics to describe a politician that takes inconsistent positions on an issue or set of issues. It is used to paint a politician as untrustworthy on an issue or in general. I have never heard it used outside of a political discussion.

Examples:

"I don't like him because he flip flops on every issue, he has no core values"

"She flip flopped on the war"

"They flip flopped on abortion"

Thanks for all the contributions. Yes Aaron and Cole, I think you are both right regarding the negative connotation that the expression conveys. From what I have read you can also use it when referring to changes in company policy too.

Karen thanks too on your idea on a possible origen of the word, it sounds plausible...

Keep ideas rolling in..