What in the world is infrared radiation

Infrared radiation is heat that travels from one place to another
in the form of electromagnetic waves.

It's called "infrared" because its wavelength is just past the
longest visible light ... the next category with wavelengths
longer than red light.

Infrared radiation is how heat gets here from the sun, and how
you feel the heat from a fireplace or a campfire when you stand
20 feet away from them.  When that happens, your front gets
toasty while your back stays cold, so you know it's not a matter
of any warm air around you that's warming you.  It's the infrared
electromagnetic radiation direct from the fire to your skin.

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.