x86 Instruction Set Reference

WAIT/FWAIT - Wait

Opcode Mnemonic Description
9B WAIT Check pending unmasked floating-point exceptions.
9B FWAIT Check pending unmasked floating-point exceptions.
Description

WAIT/FWAIT: Wait (x86 Instruction Set Reference)
Operation 
CheckForPendingUnmaskedFloatingPointExceptions();
FPU flags affected

The C0, C1, C2, and C3 flags are undefined.