Network and addresses
Subnet and CIDR
An address range notation like 192.0.2.0/24: the number after the slash is the mask length.
CIDR defines a block of addresses: /32 is one address, /24 is 256 addresses, /64 is the standard IPv6 subnet per server. Providers describe extra IPs and IPv6 subnets this way.
The subnet calculator helps work out the range, the mask and the number of addresses.