Laptop power connector
You can either use the power cord or the battery with a laptop. Many people will use the power cord while the laptop is on an unsteady position, such as in someone's lap.
You should only use the power cord when the laptop is on a steady position such as a desk or a table. When the laptop is on someone's lap or some place not steady, the power cord gets bumped or pressure is applied where it is plugged into the computer. It doesn't seem like a big deal. However this weakens the port the power cord is plugged into.
These bumps over time will eventually cause the port to fail. This port is part of the motherboard. If the warranty has expired, the replacement of the motherboard can be expensive and my be cheaper to replace the laptop than to replace the motherboard.