Its sort of the same thing. Human relationships are like family, boyfriend and girlfriend, classmates. Human relations are the relationship between people, but its a more professional word used in textbooks for learning and work settings.

Human relationships are, collectively, all the individual relationships between people. I have a relationship with my mother, aunt, wife, friends etc. Relationships are measurable, countable etc.; everybody has them, and the concept is readily understood by everybody, though different people may classify them in different ways. Human relations is a far more abstract term meaning 'interactions between people' in a very general sense. Some academics like to use it because.it can mean almost anything.

Human relationships are like family, friends, or even co-workers or bosses/employees. It's a connection between two people. Human relation an mean the same thing, but its most often used in a professional setting. A human relations, or HR, department at a company is responsible for maintaining a professional atmosphere within a company and often times responsible for maintaining the appearance of professionalism publicly in cases of scandal. Also, if you have a relationship with someone, it means you have some kind if connection with them, and can be used informally to imply a romantic relationship with the person. If you say you are having relations with someone, it's a little bit outdated, but it has the connotation that you're having sex with that person.