In general, in many programming languages Float is used as a synonym for Single: a 4 byte word holding a floating point numeric value in single precision, according to IEEE 754.
It is assumed that this is also true in the context of macros: the function ActionScript.SetProperty.Float requires a single value in order to set a float property. Also, the MSDN article on floats states:
The corresponding .NET Framework data type is Single. The properties and methods of the float data type are the same as the Single properties and methods.
Again, you'll rarely have to explicitely give a float value - if at all, you need to know wich property holds a float, and pass it accordingly.