An internship is normally an unpaid position within a company or organisation. It differs from voluntary work in that it is normally more structured and more focused, often with specific job responsibilities, outcomes and goals.
Although unpaid, some organisations do offer a type of stripend, although this is normally fairly minimal, and are likely to offer expenses as well.
Internships originated in political circles, where they were seen as an opportunity for people to gain valuable experience within a political organisation, in return for the voluntary work they did for that party.
The idea of internships moved into the commercial sector quite slowly, but has gathered pace over the last few years. In some industries it is rife, and has come in for a lot of criticism for the way it has developed as a working practice.
The reason internships have come in for a lot of criticism, is that increasingly they are seen as being quite exploitative. From a company point of view it means they can use unpaid staff, who have no or very few legal rights or benefits, to do jobs that the company would otherwise have to employ people to do.
From the point of view of someone looking for a job, if there are few job openings, but there are some internships, people may feel pressured or obligated to go down that route, in order to gain experience, and hopefully get a job at the end of it
It is worth making a distinction between internships and placements. Many university and college courses do offer some element of practical experience. This sometimes is done as a placement within an organisation, or in a virtual setting with some type of online laboratory.
When it is done as a placement within an organisation it is a perfectly legitimate use of resources, both for the organisation and the university.
Whether an individual should apply for a cyber security internship is really a question only they can answer. It may well depend to an extent on how desperate they are for a job or work experience.
This desperation, can of course only act to feed the more immoral employers who sees internships as a way of cheap or unpaid labor.