Usually references are the previous landlord you dealt with. If that was already covered, then personal references, people who know how you live, what you do, etc. This is not someone from your place of employment. You can use your parish priest, a fellow renter, a neighbor, etc.
Choose people that can attest to the fact that you have performed well at your current job for a certain amount of time or that you have demonstrated a great deal of personal responsibility in other ways. A career mentor since the experience with you is of primarily a professional nature, can speak about your good qualities and your ability to handle responsibilities and pressure. A professor, a boss at a job you’ve been working at for at least six months (as long as your boss is satisfied with your work, attendance and attitude). A work or volunteer supervisor.
When it doesn't specify, you can choose which type of reference.
I would choose one friend and one business employer.
Personal
Put down someone you know will say glowing things about you.
Someone they could contact if you bail on them, a relative, an employer, etc...
I'm filling out this rental application for my husband and I. It asks for references, but it does not specify which type of reference, such as credit or personal. What type of reference should I assume they are asking for? It's already asked for our current landlord's information in another section.