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Insolation (or solar irradiance) is the amount of solar EMR energy striking a given amount of surface during a given time interval. It is sometimes specified as a power (energy rate) per unit surface area (more often when the form solar irradiance is used), but also often as energy per unit surface area, though in this latter case it is often cited with a specific time period in mind, e.g., a day, and the implied rate is what is arguably what's of interest. Some "energy-oriented" units:
A "power-oriented" unit is watts per square meter.
The amount is dependent upon the distance from the Sun and the angle at which it is striking the surface and is of particular interest regarding solar power generation on Earth, as well as its effect on temperature and weather.
The term is also used for off-Earth situations, i.e., other solar system bodies and sometimes for extra-solar planets regarding radiation energy from their host star, though I presume the syllable sol indicates EMR from the Sun, and the word insolation was originally coined for sunlight. The word instellation has been used for the analogous quantity from some other star, e.g., on a planet that it hosts, but the word instellation has non-related meanings as well.