the amount of energy transmitted (as by acoustic or electromagnetic radiation)
"he adjusted the intensity of the sound"
"they measured the station's signal strength"
high level or degree; the property of being intense
"The intensity of the sunlight made it impossible to read without wearing sunglasses."
chromatic purity: freedom from dilution with white and hence vivid in hue
"The intensity of the sunset's orange made the clouds appear incredibly vivid against the deepening blue sky."
The quality of being intense.
"The intensity of the storm caused everyone to seek shelter immediately."
In plain English: Intensity is how strong, powerful, or extreme something feels at any given moment.
"The intensity of the sun made her wear sunglasses outside."
The word intensity comes from combining the adjective intense with the suffix -ity. It entered English through Medieval Latin as a noun form derived from this same root.