Which of the following is an essential element of a finished basement?

The presence of electrical outlets for usage is indeed an essential element of a finished basement. When finishing a basement, one of the primary considerations is to ensure that the space is functional for everyday activities. Electrical outlets enable the use of lighting, appliances, electronics, and other devices necessary for a comfortable living area. Properly placed outlets also help to prevent the use of extension cords, which can create safety hazards.

In the context of the other options, while connections to the main water supply, large windows for natural light, and a dedicated HVAC system are important aspects of a well-designed and comfortable living space, they are not strictly required for the basement to be considered "finished" per se. The term "finished basement" typically refers to the aesthetic and practical usability of the space, which heavily relies on access to electrical outlets for its overall functionality.