An adult learner (North America) or mature learner (UK) (sometimes also called adult student, returning adult, and adult returner) is a person who is 25 years and up who is involved in forms of learning.
- Delays enrollment (does not enter post secondary education in the same calendar year that he or she finished high school).
- Attends part time for at least part of the academic year.
- Works full time (35 hours or more per week) while enrolled.
- Is considered financially independent for purposes of determining eligibility for financial aid.
- Has dependents other than a spouse (usually children, but sometimes others).
- Is a single parent (either not married or married but separated and has dependents).
- Does not have a high school diploma (completed high school with a GED or other high school completion certificate or did not finish high school).
It should be noted that not all non-traditional students are adult learners, as the term refers to the brain development of the person, but adult learners are considered non-traditional students. This can be due to the wide range of cultural, job, and educational backgrounds. 
In the UK, a student is normally classified as a mature student if he or she is an (undergraduate) student who is at least 25+ years old at the start of his or her course, or in the Irish case on the first of January of the year of entry, and usually having been away from school for at least two years. The normal entry requirements for school-leavers wishing to start an undergraduate degree are often not applied to mature students.
In higher education
Adult learners seem to be overtaking traditional college students in the age range of 18-22 in the higher education arena. The NCES noted in a 2002 study that nearly three quarters of American undergraduate students met one of the above characteristics for classification as a nontraditional student; of those, 46% were so defined because of delayed enrollment. In 2008, 36 percent of post secondary students were age 25 or older (Adult Learners) and 47 percent were independent students.
More than half of nontraditional students enroll in two-year institutions, and the more nontraditional they get (i.e. the more characteristics of the above list they display), the more likely they are to consider themselves working adults first and students second. According to WorldWideLearn.com, which cites research by educational journal Recruitment & Retention in Higher Education, the average adult learner is a 35-year-old, married, middle-class Caucasian mother.
Studies in the UK have explored the ways in which classed, gendered and relational positionings can conflict with adult learners' education trajectory; often contributing to their withdrawal from academia.
As opposed to a child or adolescent, adult learners typically have more life experience and their brains are more fully developed. When confronted with new knowledge or an experience, adult learners construe new meaning based on their life experiences and their more developed brains process these experiences differently than someone with a less developed brain (children and adolescents).
- Brookfield, S.D. (1991). Understanding and Facilitating Adult Learning: A Comprehensive Analysis of Principles and Effective Practices. 2nd edition. Jossey-Bass.
- Crimaldi, Laura, "Older residents follow Pathway to college", Boston Herald, Sunday, January 4, 2009. About students successes in the College Pathways program at ABCD Learning Works in Boston, Massachusetts.
- Galbraith, M.W. (2004). Adult learning methods: a guide for effective instruction. 3rd edition. Krieger Publishing.
- Rogers, Alan, "Non-formal Education: Flexible Schooling Or Participatory Education?", Springer, 2005. ISBN 0-387-24636-3
- "Who is the Adult Learner? - Southern Regional Education Board". www.sreb.org. Retrieved 2017-06-21.
- Special Analysis 2002 - Nontraditional Undergraduates Archived April 16, 2007, at the Wayback Machine.
- "Yesterday's Nontraditional Student is Today's Traditional Student" (PDF). Center for Law and Social Policy. Retrieved 2010-08-09.
- Mannay, D. and Morgan, M. 2013. Anatomies of inequality: Considering the emotional cost of aiming higher for marginalised, mature, mothers re-entering education. Journal of Adult and Continuing Education. 19 (1), pp. 57-75.http://manchester.metapress.com/content/7q4h6576268w7602/[permanent dead link]
- Merriam, S. B., & Caffarella, R. S., & Baumgartner, L. M. (2007). Learning in adulthood (3rd ed.). San Francisco: Jossey-Bass.