Love is an emotion that can be expressed about any lifeform, inanimate object, time period, or spatial area. It is typically associated with affection, compassion, happiness, and when between people, sexual attraction. For Humans, it can be one of the strongest feelings one individual has for another and lead to procreation.
Captain Montgomery Scott once expressed his love for starships, particularly the USS Enterprise, by using an analogy about females, stating "You don't ever love a woman quite the way you did that first one." (TNG: "Relics")
Love in media
In the 24th century, holoprograms involving love existed like Vulcan Love Slave, and the sequels, Vulcan Love Slave, Part Two: The Revenge and Vulcan Love Slave, Volume Three. (DS9: "The Ascent", "Doctor Bashir, I Presume", "The Emperor's New Cloak")
Love in potions
In 2269, Harry Mudd tried to sell love via means of love potion crystals. Although the effects of the potion were temporarily effective, once they wore off, the resulting emotions between the involved individuals turned to hate. (TAS: "Mudd's Passion")