Q.  What is Dark Matter, really?

A.  It's all sorts of planets and other smaller bodies lying outside solar systems.

Q.  Why is it called Dark?

A.  Because it's too cold to give out its own light, and too distant from any star to be visible by reflected light.

Q.  Then how do we know about it?

A.  It includes a lot of mass -- perhaps 90% of a galaxy's mass. This affects the rotation of galaxies, which can be detected.

Q.  Can it be detected directly?

A.  Yes, even very cold bodies radiate, but with Dark Matter this radiation is of long wavelength, in the microwave band.