There are a number of timing constraints that apply to flip-flops (or other elements) that are all relative to the same clock signal. These are called intra-clock constraints, or timing, etc.
Sometimes there are timing paths or constraints that cross from one clock to another. These are called inter-clock constraints, or timing.
For example, you can have a skew defined for one clock (intra-clock skew) or you can define the skew between two or more different clocks (inter-clock skew)