Call of Duty: Modern Warfare 2 (2009)

If you haven't entered into the special ops yet and are curious what this achievement means, let me give you a quick breakdown.

Basically there are special missions called special ops. These all have specific mission objectives. You can choose what difficulty you want to complete each special op mission on. The difficulty will specifically relate to how many stars you get upon completion of the mission. The max you can is 3 stars for beating the special op mission on the hardest difficulty. Therefore, this achievement, you can either play 7 missions at the hardest difficulty or some combination of the other difficulties.

Since there are other achievements related to this, the ultimate goal should be completing each special op mission on veteran difficulty to obtain 3 stars on each one.