The Love Square is what is commonly referred to as the four most popular pairings, or "ships," in the Miraculous Ladybug fandom: Adrienette (Adrien Agreste x Marinette Dupain-Cheng), Ladien (Ladybug x Adrien), Ladynoir (Ladybug x Chat Noir), and Marichat (Marinette x Chat Noir).
While Marinette and Ladybug are the same character, similarly to how Adrien and Chat Noir are the same character, these four ships take place between two people as a result of how they portray themselves with or without their powers. Marinette may be clumsy in both common clothes and costume, she is far more confident in red and black than she is as a common person. Likewise, Adrien is a struggling person with mental health issues, but appears to be able to conceal them better with staff in hand. The mix of personality types usually determines the flavor of the pairing as a whole, so the Love Square is a very stable way to process the interactions between Miraculous Ladybug's lead protagonists.
The people of Miraculous Ladybug fandom can create fanon that distorts the fact that each of these Love Squares are either one-sidedly romantic or simply platonic, creating romantic, sensual, and even sexual relationships between the two. However, the canon will most likely always keep Marinette/Ladybug and Adrien/Chat Noir more than friends yet less than lovers.