Definition from buildingSMART: A defined type of simple data type REAL (required since a select type, i.e. IfcSimpleValue, cannot include directly simple types in its select list). In principle, the domain of IfcReal (being a Real) is all rational, irrational and scientific real numbers. Here the precision is unconstrained, but in practise it is implementation specific.
HISTORY New type in IFC Release 1.5.1.