How does memory shares works?

Hello!

So i as studying how Resource Pools works with share and one thought came to me. How does share works for memory? I can see how it works for CPU. Every time a virtual machine needs to use the physical CPU it will get scheduled to do so. If it has more shares, it will get more more chances to get the physical CPU in a contention situation. But i'm finding hard to understand how it would work for memory. In a contention situation, the virtual machine with high shares for memory would get more memory from where?

Can someone please clear this out for me?

Thanks!