Evil eye is the belief that someone looking at you with envy or jealousy can bring you misfortune or lead to you losing the thing, object of the envy.
The idea of someone looking at you can be more widely understood as someone focusing their attention on you with malicious intent, envy, or jealousy.
That can also happen unintentionally. It is sometimes even believed that it could even be the person afflicted to have brought the Evil Eye on themselves.
Anthropologist have identified a few recurring features with regards to the Evil Eye:
1) Its power comes primarily through or from the eye, with touch or speech, in particular oral praise.
2) The person, animal or object stricken is desirable or of value.
3) Its action is typically immediate, though the effects may manifest over time or after some time.
4) The person cursed by the Evil Eye may not be aware of it or of what caused their affliction.
5) It's not always preventable. But the effects can be sometimes deflected, with the help of charms, gestures, amulets, objects or symbols.
In some countries like Egypt, Morocco and Spain there's a talisman called Hamsa, this ancient talisman (820 BCE) helps against the Evil Eye and other misfortunes.
In Southern Italy (specifically the Neapolitan area) the most common folk practice to protect against the Evil Eye is the horn, either the amulet or the horn gesture (pointed downards to hell)
Other common Evil Eye solutions are throwing salt behind your back and leaving a hanging garlic to dry out.
I'm not sure where the Evil Eye originated from, it could be from ancient Mesopotamia, Rome or Greece.
When I was in Mexico, there was also a lot of culture regarding the evil eye, more than in Spain, as you mention in your article, in Spain there is a lot of evidence of this curse, I have never heard of people who feel that they have been given an evil eye in Spain...