is there anybody who knows IM3 and H3?

is there anybody who knows IM3 and H3? how can they get ?
Pls make a expression in detai, any thanks!

IM3= 3rd order inter modulation?
H3 = 3rd harmonic?

assume using two sources with frequency fo and ft as input signal to the device, due to the nonlinearity, both fo and ft will mixes with different degree. less say, fo1, fo2, fo3.... / ft1, ft2, ft3... are the harmonics of the input signals, fo1(+-)ft1,ft2,..., fo1(+-)ft1,ft2,..., ...., than the first signal's harmonic will mix with the second signal's harmonic. Less assume again the DUT (device under test) are narrow band, IM2=fo1(+-)ft1 will be out of band and won't affect the DUT performance. however, IM3=fo1(+-)ft2 will be fall into the desired band and couse distortion. Hence, it is a serious one, in common case.

eg.
fo1=900MHz, ft1=901MHz,

IM2 =900+901=1801,
=900 -901=1,
IM3 =900+1802=2702, (first harmonic mixes with second harmonic)
=900 -1802=902,(in band!)