Question

what is dark matter

Answer 1

dark matter to put it simply is the stuff that keeps the galaxies bounded(not spreading loosely) and hypothetically it is said that weakly interactive massive particles(WIMPS) is what dark matter is made of but don't count on that because we haven't tested Super symmetry to a good extent yet

Answer 2

"Dark" matter is not necessarily dark but has been given that name because it is not known what it is. It cannot be seen and so far can't be detected. The only evidence it exists is that something is in and around our galaxy (the Milky Way) and all other galaxies that allows them to rotate in the manner they do - too fast and disproportionately so the farther out from the center one measures. All major galaxies are rotating at a rate, and especially the outer arms, that is not possible (within our current understanding of either General Relativity or Newtonian physics) unless there is far more mass than we can detect. The "Dark" in Dark Matter also does NOT include gases or dust particles that might appear dark when looking at visible light or other wavelength photos - we can detect those.
By observing other galaxies, astrophysicists have determined that Dark Matter is so prevalent that its total mass is more than 5 times as much as the total ("atomic") mass we can account for in the universe. Atoms (and the forms of energy related to atoms and the universe as we know it) are currently thought to represent slightly less than 5% (4.9) of total matter and energy of the universe. Dark Matter (not energy but having mass) is thought to make up almost 27% (26.8) of the total Mass and Energy of the universe. Dark Energy makes up the difference of nearly 75% (about 73.3)
Not only is Dark Matter needed to explain the rotational characteristics of galaxies, it also is needed to properly model the formation of clusters and strings of galaxies throughout the visible universe.
As it (so far) cannot be detected, many theories have been used or postulated as to what Dark Matter may be. @mathaddict4471 has mentioned one of the most popular theories, that of WIMPs.
Finally, whatever it is that does make up Dark Matter, it is not considered that it will relate to Dark Energy. Dark energy seems to spread fairly evenly throughout the universe and does not concentrate in or around either known matter or Dark Matter. The word Dark for Energy "means" the same thing as for Matter, that is "Dark" Energy so far cannot be seen or otherwise detected - what it is and, therefore the reasons for these two phenomena, have not "come to light". "What Dark Matter and Dark Energy is" is considered by most in the field of cosmology the most important questions currently facing cosmologist.