Apraxia is defined as:

Apraxia is characterized as the inability to plan and execute purposeful motor activities, despite having the physical ability to perform them. This condition affects the coordination required for voluntary movement, leading to difficulty in carrying out tasks or movements that are commonly known and understood. Individuals with apraxia struggle with the sequencing of movements necessary for tasks, whether it be simple actions like brushing teeth or more complex activities.

In this context, the other options describe different conditions or capabilities. The inability to understand language pertains to aphasia, which relates to comprehension rather than motor planning. Recognizing faces is associated with prosopagnosia, whereas the inability to express feelings relates more to emotional or psychological disorders. Therefore, the definition that aligns with apraxia's characteristics is the difficulty in planning and executing motor activities.