One of the leading candidates for dark matter is a type of particle that can have weak and gravitational interactions, but does not have electromagnetic or strong interactions. Such a particle is called Weakly Interacting Massive Particle (WIMP). On average at most one WIMP interacts with the human body per minute, although billions of them can pass through the body every second.
Many observational evidences suggest that galaxies contain an invisible form of matter which does not interact electromagnetically. The total mass of a galaxy can be measured from the velocities of the stars that orbit the center of the galaxy. We can measure the mass of the luminous part of galaxies, and thus can estimate the remaining mass which is invisible and is called dark matter. Dark matter is estimated to be more than 5 times the ordinary matter in the universe.