What is the usual netmask?

Could you elaborate on the concept of a netmask and provide a typical example of what it might look like? In the realm of networking and IP addressing, a netmask serves as a crucial component for determining the network segment and host portion of an IP address. Understanding its function and format is essential for effective network administration. So, could you explain in simple terms what a netmask represents and give a common netmask value that is frequently encountered?