Skimming and scanning are usually considered speed-reading skills because they are not used for intensive reading. They are essential skills nonetheless, and students need to know that sometimes intensive reading is not necessary.
Skimming a text involves running your eyes over it quickly to get the main idea. It also allows you to identify which parts of a long text you might want to read more closely. This skill is particularly useful, for example, for Business English students who have to read long reports that are several pages long. By skimming the report, they can still follow the gist and stop when they find something of particular interest to them.