What is 2³², and why is it a landmark in networking?

4294967296 — about 4.29 billion, the size of the IPv4 address space (and the range of a 32-bit unsigned integer).

The story: rain soaks a bear on the beach; it holds up a gun on a second beach.

IPv4 addresses are 32 bits, so there are 2³² ≈ 4.29 billion of them — famously too few, which drove NAT and IPv6. It's also the max for a 32-bit unsigned int (0 to 4294967295). Remember it as "4.3 billion"; the exhaustion of this pool is why your home router hides many devices behind one public address.