Are Made In and Country of Origin the same thing?

Question

1. Are Made In and Country of Origin the same thing? Which term should be used on the product and which on a commercial invoice?
2. Whilst we are still in the EU can country of origin be the EU or does it have to be a specific country?
3. Does the location of the final operation determine country of origin or is there a weighting for the amount of work done in different countries. i.e. if we send items to Madagascar for some finishing operations can the country of origin still be UK or will it automatically become Madagascar? is there a formula for working this out?