Below is the United States Department of Education definition of an English learner.
The term “English learner,” when used with respect to an individual, means an individual —
(A) who is aged 3 through 21;
(B) who is enrolled or preparing to enroll in an elementary school or secondary school;
(C) (i) who was not born in the United States or whose native language is a language other than English;
(ii) (I) who is a Native American or Alaska Native, or a native resident of the outlying areas; and
(II) who comes from an environment where a language other than English has had a significant impact on the
individual's level of English language proficiency; or
(iii) who is migratory, whose native language is a language other than English, and who comes from an environment where a
language other than English is dominant; and
(D) whose difficulties in speaking, reading, writing, or understanding the English language may be sufficient to deny the individual —
(i) the ability to meet the challenging State academic standards;
(ii) the ability to successfully achieve in classrooms where the language of instruction is
(iii) the opportunity to participate fully in society.
(ESEA Section 8101(20))