It always talks about yield curve, upward, inverted blabla. My question is does it mean spot curve (Z-bond) or it means yield to maturity curve to coupon bond?
You should probably tell it to stop talking then, as you’ve got an exam to prepare for. 
When they say the yield curve is upward sloping, my understanding is that this refers to the on-the run US treasuries. additionally, the yield curve and the term structure of interest rates both behave in a similar fashion.
That is if the yield curve is upward sloping, then the term structure will also be upward sloping.
I’m not sure what you meant by yield to maturity curve to coupon bond.
I’m not sure what you meant by yield to maturity curve to coupon bond.
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If it just means T-spot curve, that makes more sense. I thought it was a portfolio with different maturaty bonds,and the curve express all YTM of those bond. Which now sounds no sense. thank you~
I suspect that she means the par curve.
Generally, when finance people refer to “the yield curve”, they mean the (Treasury) par curve. This is the curve that gives the YTM on coupon-paying Treasuries of all maturities. It’s called the par curve because if a Treasury at a given maturity paid the coupon rate given by the par curve, it would sell at . . . sell . . . par.
The (Treasury) spot curve is derived from the par curve; its values are discount rates for single payments at the given maturities, and you can think of them as the YTMs for zero-coupon bonds at each maturity. It is derived from the par curve by bootstrapping.
The (Treasury) forward curve is derived from the spot curve; its values are the single-period (six-month) discount rates for a single payment at maturity; a payment 3 years from now would be discounted back to 2½ years at the 2½-year rate on the forward curve.