What term describes someone who is lacking the ability or skill to perform effectively?

The term that describes someone who is lacking the ability or skill to perform effectively is "ineffective." This term is used to characterize an individual who does not produce the desired or expected results due to insufficient skills, knowledge, or competency in a specific area. When someone is labeled as ineffective, it implies that their performance falls short of what is required or necessary for a particular task or role.

In contrast, terms like "competent," "capable," and "proficient" refer to the presence of skills and effectiveness. "Competent" denotes a level of ability sufficient to perform a task successfully, "capable" indicates the potential to do something, and "proficient" reflects a high degree of skill or mastery. These words suggest that the individual has the necessary qualifications or abilities to perform tasks effectively, highlighting their effectiveness rather than a lack thereof.