Means the hard disk is being accessed. This is the symbol for a hard disk since it was invented around 1965.
An example of this (and other) symbols used in flowchart diagrams in the IT: http://www.breezetree.com/articles/flow-chart-symbols.htm
Kees
I just purchased a Dell Inspiron 5520 and wanted to know what this light means as it keeps on flickering.
http://i.imgur.com/1hLZb.jpg
Specs: Core i5 (3rd Gen) - 3210M
4Gb RAM

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