What Does "Ese" Mean?
As a term of address, this term was popularized in Spanish-speaking regions of the United States. The word on the street is that it came about as a shorthand way for speakers of Mexican Spanish to say ese vato or ese güey (that dude).
While not commonly used in Mexico, you're quite likely to hear it in California, for example. But, ¡aguas! (be careful!) In some parts of California ese is used by members of certain gangs to self-identify. Most of the time, though, it just means dude or bro.
Check out these examples of ese.