The term first-generation can refer to either people who were born in one country and relocated to another at a young age, or to their children born in the country they have relocated to. The term second-generation refers to children of first-generation immigrants, and thus exhibits the same ambiguity. The term 1.5 generation is a term coined for people who identify as "first generation", yet lack the necessary acculturation.
The term first-generation, as it pertains to a person's nationality or residency in a country, can imply two possible meanings, depending on context:
This ambiguity is captured and corroborated in The Oxford English Dictionary's definition of "generation":
In the United States, among demographers and other social scientists, the term "first generation" is used to refer to foreign-born residents (excluding those born abroad of American parents).
There is no universal consensus on which of these meanings is always intended.
The term 1.5 generation or 1.5G refers to two types of people. Individuals who immigrate to a new country before or during their early teens (Asher 2011). They earn the label the "1.5 generation" because they bring with them or maintain characteristics from their home country, meanwhile engaging in assimilation and socialization with their new country. Often times, in the case of small children, a battle of linguistic comprehension occurs between their academic language and the language spoken at home (Asher 2011). Their identity is thus, a combination of new and old culture and tradition. Sociologist Ruben Rumbaut was among the first to use the term to examine outcomes among those arriving in the United States before adolescence, but since then the term has expanded to include foreign students, as well as other unique individuals.
Depending on the age of immigration, the community where they settle, extent of education in their native country, and other factors, 1.5 generation individuals identify with their countries of origin to varying degrees. However, their identification is affected by their experiences growing up in the new country. 1.5G individuals are often bilingual and find it easier to assimilate into local culture and society than people who immigrate as adults. Many 1.5 generation individuals also, become bi-cultural, combining both cultures - culture from the country of origin with the culture of the new country.
The term "second-generation" extends the concept of first-generation by one generation. As such, the term exhibits the same type of ambiguity as "first-generation," as well as additional ones.