As a non-native speaker I am having some trouble distinguishing between the two words "merge" and "merger". To me, it sounds like "merger" describes a major event, often occurring between legal entities such as companies, countries, pieces of industry,... In computer science, I have more often seen merge used as a noun, e.g. if in a version control system two branches are merged, the result is called a merge. The process while it is occurring is also called a merge.
Are the two terms interchangeable, or are there clear distinctions in usage (in general practice)?