How many hosts are available in a /27 subnet?

What is prefix length?

What is a subnet mask?

What does /24 mean?

It tells you how many bits of the IP address belong to the network portion.

What is a network ID ?

A network ID (or network address) identifies the subnet itself, not a specific device.

It is the first address in a subnet and is used by routers and devices to know which network an IP belongs to.
Example:192.168.1.0