What is a sudden flash of brightness observed over the Sun's surface known as?

The phenomenon referred to as a sudden flash of brightness observed over the Sun's surface is specifically known as solar flares. A solar flare is an intense burst of radiation resulting from the release of magnetic energy stored in the Sun's atmosphere. This energy is released in various forms, including light and heat, which can manifest as a sudden and dramatic increase in brightness that can last from minutes to hours.

Solar flares are significant because they can affect space weather, influencing satellite operations, communications, and even power grids on Earth. The other options do not describe this phenomenon accurately: solar flashes and solar fusion do not refer to recognized astronomical terms related to brightness on the Sun's surface, while solar spots are dark regions on the Sun’s surface associated with magnetic activity but do not exhibit the sudden intensities of light that characterize flares.