Weakly Interacting Massive Particles, or WIMPs. (little scientific, might not be asked)

• Dark matter is an invisible form of material that's thought to exist because scientists have observed its apparent gravitational effects on galaxies and galaxy clusters. Scientists estimate that the mysterious substance makes up almost 80 percent of the matter in the universe.
• So far no one's been able to pinpoint the particles that make up dark matter. But a leading candidate is a theoretical group known as Weakly Interacting Massive Particles, or WIMPs.
• As the name implies, these hypothetical particles would have only a weak effect on regular matter—they typically zip straight through most of the stuff in the universe, including people. But WIMPs of certain masses can collide with atomic nuclei on occasion—and now it appears such collisions might happen more often than previously thought.
• According to theory, WIMPs were created at the dawn of the universe, just like other forms of matter. Although WIMPs don't interact much with normal matter, if two of the particles strike each other, they annihilate—all their mass turns into energy.
• Models suggest that today billions of WIMPs are streaming through Earth and its inhabitants every second.
• Because WIMPs don't have strong effects on normal matter, collisions inside the human body shouldn't pose much danger.