Light is a form of energy. What we call light is a small part of the electromagnetic spectrum which includes ultra violet and infrared as well as radio waves and microwaves. All these things are basically the same but we can only see a small section of the whole lot (spectrum). This make sense, when we were evolving the only radio waves on the planet would have come from the stars or lightning. Not helpful to see only those things when a predator is creeping up on you. The difference between all these parts of the electromagnetic spectrum is their wave length and our eyes evolved to see the most useful wavelengths around on this planet.
Remember light travels in straight lines (unless it goes past a star or black hole when they can be bent). In space light travels at 300,000,000 m/s around a million times faster than sound travels through the air.
Luminous objects are light sources they give out light.
Materials can be described as transparent (let's through all the light), translucent (let's through some light) or opaque (let's through no light). Remember the thickness of the material is important! One sheet of paper is translucent but 100 sheets will be opaque. We also need to know about reflection, refraction and dispersion which are coming in the next post.