They are called EMU (English Metric Units)
http://en.wikipedia.org/wiki/English_Metric_Unit#DrawingML
http://polymathprogrammer.com/2009/10/22/english-metric-units-and-open-xml/
1pt = 12,700 EMU
Also as explained here 1px =~ 9525EMU
http://openxmldeveloper.org/discussions/formats/f/15/p/396/933.aspx