Additional income is income you make apart from you main occupation. This can range from scrapping metal to babysitting. Depending on what you do for this additional income, you may or may not have to pay taxes on it.

I believe Rent Income or "rental income" is any income received from a property you own & have tennants in who pay you "rent" to live there. This is usually considered a form of income, obviously depending on the country you live in.

The low income classification is based on monthly income and the number of people in your family,depending on your family size 2800 may qualify as low income.

Depending on which country!

Zoology has an income of about $40,000 a year (depending on your level of study) and wildlife biology has a yearly income of about $50,000, again, depending on your level of studies and what not. But zoology is pretty much just a branch of wildlife biology.