The word interest is used very often in debates. There are two main uses. The first one would be "in your interest" or "in the country's best interest", meaning you do something to help a group of people, usually the voters. For example: "In the country's best interest, we need to pass this law".
The second one would be "to have interests" in something. For example: "A foreign government has interests in Saudi oil", which means they want to take advantage of an opportunity to expand their economy or improve their position.
This second meaning leads to an expression that has been very common over the last few years: "conflict of interest". It means a public servant may have some business in the private sector that could prevent them to rightfully represent the people's best interest. For example: "The governor claimed that owning a car company would not lead her to cut funding for public transport".