Is a lady with height 5.6 n weight 73 fat?

noooo, she's VERY underweight, actually 73 lbs. at 5'6'' is dangerous! looks like she'll need to gain some weight.

If you meant 73 Kilos, then you might be considered slightly overweight, certainly not morbidly obese, but it really depends upon your body type. You should consult a physician or perhaps a nutritionist about what your "ideal" weight range should be. Definitely don't try to compare yourself with the usual "anorexic, airbrushed" women you see in magazines and on TV. They are icons for "attractiveness" (if that's what you want to call it) and not for true health and beauty.