What term describes a fuel/air mixture that lacks sufficient fuel?

The term that describes a fuel/air mixture that lacks sufficient fuel is "too lean." In combustion processes, a "lean" mixture means that there is a higher proportion of air compared to fuel. This can lead to inefficient burning and potential issues such as incomplete combustion, which can produce harmful emissions and reduce overall efficiency. A lean mixture can also cause the engine to operate poorly, as it may not generate enough power for optimal performance. Understanding the concept of a lean mixture is crucial for those working with fuel systems, as it can greatly affect both safety and efficiency in various applications.