Meaning: to lose visual contact, but also stop having contact, relation with something.
Perder → to lose
Vista → sight
Sentence examples:
No pierdas de vista a los niños, en esta calle hay muchos coches / Keep an eye on the kids, there are many cars in this street.
Hace tiempo que no veo a Juan, desde que se mudó lo perdí de vista / It’s been a long time without seeing Juan, since he moved out I “lost track of him”.
Sometimes we use it to emphasis something we don’t want to overlook:
No pierdas de vista a esta banda, pronto serán famosos / Keep an eye on this band, they soon will be famous.
Or also as an angry way of telling someone to go away
No quiero hablar más contigo ¡piérdete de mi vista! / I don’t want to talk to you anymore, get out of my sight!