Shon-ha'lock, or "the engulfment", was the Vulcan term for what Humans called "love at first sight".
In 2373, Tuvok characterized Harry Kim's feelings for Marayna as shon-ha'lock. As Marayna was believed to be a hologram at the time and thus no relationship was possible, he recommended logical deconstruction followed by meditative suppression. Tuvok described shon-ha-lock as the "most intense and psychologically perilous form of eros". (VOY: "Alter Ego")
When he was young, Tuvok experienced shon-ha'lock towards Jara, the daughter of a Terrelian diplomat. He overcame those emotions under the tutelage of a Vulcan master. (VOY: "Gravity")