"During the course of a year" basically talks about the passage of time during that year, in relation to the events that have happened or are continuously happening during that year. for example : Your medical insurance will cover you during the course of your employment. Meaning whilst you are employed, your are insured for medical related issues but once you are not employed anymore its over. or if I said "During the course of a year, the company A will have to complete its merger with company B" meaning that there is no specific date that the companies have to merge but rather they will have to do it bit by bit over the time frame of 1 year. But in my opinion it does depend on the context as well, as I would prefer to say "Over the course of a year" Hope this helps ^-^