The ping of death is a DoS attack in which the target host is flooded with malformed IP packets. These packets often come in the form of ICMP ping traffic. IPv4's total length field is a 16-bit field, implying a maximum packet size of 65,535 bytes. Early implementations of the TCP/IP stack did not fail smoothly in the event of oversized packets. Ping of death also managed to overwhelm simple bounds checking for single packet size by inserting a long series of IPv4 fragments into the inbound buffers. When the target system tried to reassemble the packets, its TCP/IP stack would crash.
Ping of death represented a serious threat in the Windows 95 era. Since then, updated OSs rule it out. Also, the normal firewall configuration of dropping ICMP in general or IP fragments in particular will prevent it.