Literally meaning “tying together”, this word can be used to refer to the relationships that tie humans together, in particular romantic relationships.
In Japan (as well as China and Korea) lovers who are destined to be together are thought to be joined by the “red thread of fate”. Romantic partners are often depicted with a red thread connecting their little fingers.
On a broader note, musubi essentially refers to the interconnecting energy of the universe. Japanese kami (divine spirits) are thought to be manifestations of this energy.