When it comes to describing something or someone that is "below average," there are various synonyms you can use. Some of these include mediocre, inadequate, substandard, inferior, unsatisfactory, and lackluster. Each of these words has its own nuances and connotations, which can help you choose the best one for the given situation. For example, you might use "mediocre" to describe a meal that was neither excellent nor terrible, while "inadequate" would be more appropriate to describe a job candidate who lacked the necessary qualifications. No matter which synonym you choose, the goal is to communicate that the thing or person in question is not up to par or performing as expected.