In knot theory, a Hopf link is the simplest link with more than one component. A Hopf link is created when two circles are linked together exactly once. Hence, it has a linking number of ±1 (depending on the orientation).
It is named after Heinz Hopf, a German mathematician, who discussed it in 1931 as part of his research on Hopf fibration. However, it was known to Gauss before Hopf’s work and had also been used outside of mathematics, for example as the crest of Buzan-ha, which was a “Japanese Buddhist sect founded in the 16th century“.