Scanning

You skim read material to get the general picture. You scan when looking for specific information.

You may need to find specific details on a topic for an assignment or a task that your lecturer has set. There is little point in skimming a whole book for this purpose. You should scan the text for words related to the topic. You can run your eyes down the page looking for these expressions - in chapter headings or sub-headings, or in the text itself.