A petaflop is one thousand trillion, or one quadrillion, operations per second, and represents an extremely fast computing speed for a single machine. "Flop" stands for floating-point operations per second.
In terms of today’s practical computing speed, the petaflop can also be thought of as one million gigaflops, where the gigaflop represents 1 billion floating-point operations per second. While some new supercomputers have been known to achieve multiple petaflops, more commonly available machines have not yet reached this standard.
Floating-point operations use large real numbers in a way that is efficient for the computer. In floating-point notation, exponential designations help to express the large real number in a simple way. This enables a wider range of values than in fixed-point operations, where the real number is expressed as a simple integer.