What is the default mask of a network?

Could you please elaborate on the concept of a "default mask" in the context of networking? Specifically, I'm curious about its function, significance, and how it relates to IP addresses and subnetting. I've heard it mentioned in discussions about network configurations, but I'm still unclear about its exact purpose and default value. Is it a static setting or can it be modified? Additionally, how does it impact the communication within a network? Your explanation would be greatly appreciated in helping me gain a deeper understanding of this networking concept.