The name Sancho (Spanish: [ˈsantʃo]) is an Iberian name of Basque origin (Santxo, Santzo, Santso, Antzo, Sans). Sancho stems from the Latin name Sanctius. Feminine forms of the name are Sancha, Sancia, and Sanchia (Spanish: [ˈsantʃa]), and the common patronymic is Sánchez and Sanches. Outside the Spanish-speaking world, the name is especially associated with the literary character Sancho Panza. . Sancho is a common slang term in the Spanish speaking world for the other man in the relationship. As in a spouse or girlfriend who is being unfaithful with a Sancho.
https://en.wikipedia.org/wiki/Sancho