Relevance: Is the information specialised enough for your needs?
Some sources such as encyclopaedias (both print and online, eg wikipedia) provide only brief background information on a topic. These sources are useful to get a quick overview of a topic but are not sufficiently specialised to be used as sources for your assignments.

Similarly, English language dictionaries give the meaning of words as they are used every day and not as they are used in specialised areas of study. So these also are sometimes not sufficiently specialised to be used as sources for your assignments
Most assignments require more depth and detail, so you will need to use more specialised materials such as academic books, academic and professional journal articles and appropriate web sites.

