A management fad is like a fad that people use - it's kind of like a short-term trend that is popular for a while, but eventually passes. In management, it's something that's popular, or followed, by a lot of people or companies, but isn't always a good idea and doesn't last very long. For example, some people may try a new type of management style that sounds cool and interesting at first, but it may not actually be the best way to manage things, so it doesn't stay popular for very long.