The Oxford English Dictionary definition of the word interview is "an oral examination of an applicant for a job or college place". Its origin is from the French "entrevue", from s’entrevoir meaning ‘see each other’
So there you have it - an oral examination of you, taking place face-to-face.
The word "oral" means this is about communication and the word "examination" infers a degree of in-depth questioning.
You will be subjected to questions about yourself, your skills, your experiences and your suitability as represented by you in your submitted CV. Your CV is therfore the basis of the interview.

There's a lot going on at an interview!
If you have prepared properly and know exactly what is stated on your CV then you'll have nothing to worry about. Of course, everyone worries about being asked a question they either don't know the answer to or just make a hash of it. The interviewer is unlikely to make a judgement based on one question.