An "internship" is an opportunity offered by an employer to potential employees, called "interns", to work at a firm for a fixed, limited period of time. Interns are usually undergraduates or students, and most internships last for any length of time between one week and 12 months. Internships may be part-time or full-time. They are usually part-time if offered during a university semester and full-time if offered during the summer, winter or Easter holidays, when they typically last 4-12 weeks.