"Mestizo" is one of many sometimes-ambiguous terms by which mixed ethnicity or race is described—compare mulatto, mixed-blood, metis, half-breed, Creole, bi-racial, "other."
Such identities may appear impure or threatening to either ethnic group whose members create a new person who is not exactly this or that ethnic group but a mix of both.
A multicultural society, on the other hand, may find such identities heroic, exotic, evolutionary, or pioneering; e.g. Tiger Woods, Halle Berry, Lenny Kravitz, Mariah Carey.
Oxford English Dictionary
Mestizo. A. A person of mixed European (esp. Spanish or Portuguese) and non-European parentage; spec.
(originally) a man with a Spanish father and an American Indian mother;
(later) a person of mixed American Spanish and American Indian descent.
Hence, more generally: any person of mixed racial origin.
[Cf. Canadian (French) Metis: A person having mixed white (esp. French Canadian or Scottish) and native Canadian parentage; a member of a group consisting of these people and their descendants.]
Relevance to the Renaissance:
Relevance to now, i.e. "postmodernity" or "late modernity": Following the Renaissance, the rise of nationalism and European imperialism may have imposed new legal and cultural barriers against inter-ethnic marriage in later colonies in Asia and Africa.
In early colonies in the Caribbean and Latin America, however, intermarriage among distinct or mixed ethnic groups continued.
In recent decades, improved global transportation and transnational migration have again eroded or mixed traditional ethnic or racial identities.
Relevance to multiculturalism in the USA:
Because English and other Northern European settlers and pioneers migrated with their wives and families more often than Southern Europeans like the Spanish and Portuguese, North America and the USA discouraged inter-racial marriage or legally denied its existence.
The mestizo / mestiza identity has been explored lately as a cultural alternative to the USA's traditional white-black racial polarities. (Not to disregard North American Indians, who intermarried with both white and black but with less attention . . . . )
USA culture traditionally structured society by race, defined historically by black-white racial oppositions.
Instead of a racial opposition, Mestizo (or Hispanic / Latino) identities offer a spectrum of intermingling races (including African).
Spectrum of American racial / cultural future?
Richard Rodriguez (b. 1944) is most famous for his early autobiography Hunger of Memory: The Education of Richard Rodriguez (1982), which was a popular school text and widely anthologized in the 1980s and 90s.
35 Most bookstores have replaced disciplinary categories with racial or sexual identification. In either case I must be shelved Brown. The most important theme of my writing now is impurity. My mestizo boast: As a queer Catholic Indian Spaniard at home in a temperate Chinese city in a fading blond state in a post-Protestant nation, I live up to my sixteenth-century birth.
The future is brown, is my thesis: is as brown as the tarnished past. . . .
46 A brown complexity—complexity of narrative and of desire—can be foretold from the moment Dutch sailors and African slaves meet within the Indian eye.
69 Many Americans, black as well as white, claim Indian blood. The Indian was curiously free, within the white rule, to marry both the white and the black.
[Question:] . . . It feels like American politics is caught up with the argument of your last book, “Brown,” that Latinos would shape our political future increasingly. These days we have not just Ted Cruz and Marco Rubio but both parties chasing Latino voters. How do you think this will shake out?
[Rodriguez answer:] Well I’m not sure, what you haven’t noticed in your question is that there are two prominent Latinos who are both Cuban, are both white, are both Republicans. Isn’t it interesting that the Republican Party has become the affirmative action party for the brown politician.
Where is the left on this? Where are the great brown hopes among the left?
I think what hasn’t happened yet in the official language of our political life is that we really don’t know how to speak brown-ly about each other and about ourselves. And Barack Obama is still officially designated our first black president.
Well, he’s our first brown president, which is a much more interesting thing to be because it unites these two races, but in some way what we are not able to deal with is the reality that brown is all around us.
That kids have been born, Cambodian/Mexican/German kids who don’t look like anyone who has ever lived before. And we’re still in a kind of rhetorical swamp where we’re still using the vocabulary of the 1950s: white and black America. . . .