The latter half of the 20th century seemed to inspire a pattern of designating categories of people -- categories defined initially by birth-year -- according to certain perceived shared characteristics. The most prominent such category is the Baby Boomers, which is constituted by those born right after World War II up through 1964, a date that some could argue is far too late given the introduction and social significance of the birth control pill in the late-1950s. Following the Baby Boomers is the Generation X category, those born between 1965 and 1984, and characterized by sexual liberation and social rebellion, but bleeding into the conservative backlash represented by the election to the presidency of Ronald Reagan. Next comes Generation Y, the category in question. The dates of birth of those considered to be part of this generation extends from 1985 to just about the present. "Generation Yers" are the first such category defined by the impact of communications technologies, including personal computers and smart phones, both of which revolutionized the way we live and interact.
In addition to the role of technology in defining Generation Y, other characteristics include racial diversity (the percentage of the nation's population that identifies itself as "white" is lower than ever before); political independence, signified by a lesser willingness to identify with one of the two major political parties; and economic difficulties that are viewed as representing a turning-back of the clock in terms of socioeconomic aspirations. In other words, earning power and student debts are said to be resulting in the death of the notion of each generation supplanting the previous one in terms of socioeconomic advancement.
These, then, are the principle defining characteristics of Generation Y.