Skimming is a high speed reading process and involves visually searching the sentences of a page for clues to meaning. It is conducted at a higher rate (700 wpm plus) than normal reading for comprehension (around 200-230 wpm)(sometimes known as rauding), and results in lower comprehension rates, especially with information-rich reading material.
Skimming on its own should not be used when complete comprehension of the text is the objective. Skimming is mainly used when researching and getting an overall idea of the text.
Speed reading courses which teach techniques that largely constitute skimming of written text also result in a lower comprehension rate (below 50% comprehension on standardized comprehension tests).