What does 'utmost' refer to?

The term 'utmost' refers to the highest degree, extent, or quality of something. In context, it indicates something that is at the greatest possible level or the maximum achievable standard. For example, if someone is said to have put forth their utmost effort, it means they exerted the highest amount of effort possible. This understanding aligns perfectly with the definition given in the correct answer, emphasizing the concept of being at the peak or maximum.

The other choices present contrasting ideas, such as low quality, median levels, or average abilities, which do not correspond with the meaning of 'utmost.' Therefore, 'highest in extent or degree' accurately captures the essence of the word and its usage in various contexts.