To overload is to load an excessive amount in or on something, such as an overload of electricity which shorts out the circuits. Overloading causes a "Too much!" situation.
To overload is to push something or someone too far. A supervisor can overload an employee by assigning a too much work. People can overload a bus if there are too many of them. A fuse will blow if too many appliances overload the circuits; this is called an overload (the noun form). When something gets overloaded, it usually stops working. Hair can overload or clog a sink, which will stop draining water. When something gets overloaded, there's more of something than it can handle.