quantum mechanics - What is the "monogamy principle" in entanglement?

What does the "monogamy" principle imply? At a superficial level, it seems to say that a particle can be entangled with at most one other particle.

However, I keep reading that several particles are entangled. For example:

1. 
   
   

   Quantum entanglement can reach into the past. Here they describe an experiment with two entangled pairs, $(A_1, A_2)$ and $(B_1, B_2)$. Victor is given $A_2, B_2$, Alice is given $A_1$ and Bob is given $B_1$. All three are separated by a large distance. If Victor entangles $A_2, B_2$ then he has entangled $A_1$ and $B_1$ as well. This somehow implies that each particle can be entangled with more than 1.

   
   


2. 
   

   3,000 atoms entangled in bizarre state. Scientists somehow entangled $\approx$ 3000 atoms.

   
   

Both imply that entanglement is not monogamous. So what does the "monogamy" principle actually imply?