Bible definition of ual immorality?

Hi what does the bible define as ual immorality? Im particularly interested in the before marriage issue. From the internet research Ive been doing it doesnt seem to actually say premarital is wrong but rather that ual immorality is wrong without defining it. Adultery is mentioned alot as being wrong but nothing else. Im sure I must have this wrong. Could someone with more knowledge than me please tell me what the bible says ual immorality is and please enclose quotes or a page number? Thanks