IQ or Intelligence Quotient is an attempt to measure intelligence.  This means many things to many people but generally the attribute of intelligence refers to quickness of mental apprehension (or mental agility).  It is often confused with knowledge, wisdom, memory, or a myriad of other attributes and in general has a variety of meanings depending on the context in which it is used.  IQ invariably refers to the attempt to quantify the attribute in its meaning of mental comprehension. 

There are several scales with which IQ may be measured depending upon which testing mechanism is used.  For this reason the most reliable and consistent value to be placed on IQ is that of the percentile.  An IQ of 150 is a meaningless claim unless the testing mechanism is also cited, but an IQ in the 98th percentile (i.e. higher than 98 per cent of the population) has consistent meaning.