Information: New or Secondhand?
There is a concept of time and timeliness that is important for choosing information. It's like the difference between new and secondhand. We express that by using the terms Primary and Secondary to describe sources.
Be sure to check that your sources are up to date. This is very important in some fields, like science, where information can age very rapidly. Other disciplines such as history may change very slowly, or may actually study out of date information. Your professor may specifically direct you to use sources from only the past five years.