One TeraFlops (TFLOPS) is a term for a trillion floating-point operations per second. "Tera" is a prefix for one trillion (ten raised to the twelfth power).
There's a computer called the Earth Simulator that can run at 35.86 TeraFlops. It's actually 640 supercomputers networked together, but Earth Simulator works as one computer. It's the fastest one there is.