Infons ｢情報子, jōhōshi｣ are the smallest particles and are contained within all matter in the world, including souls and even skills. Their mass is as close to zero as it gets. They are unaffected by space and time and are thus able to transfer information in any situation with zero time difference.
Observing them is extremely difficult and normally only possible under certain conditions, like inside Rimuru's stomach or an Infinity Prison. The ability to alter, combine, and abolish skills are an example of limited manipulation of Infons. Directly interacting with them is only possible as a Digital nature and a requirement to move in the Stopped World.