Definition - What does Tcpdump mean?
Tcpdump is an open-source network utility that is freely available under the BSD license. Tcpdump works on the command line interface and provides descriptions of packet content in several formats, depending on the command used.
Techopedia explains Tcpdump
Because it is a command line utility, data retrieved through tcpdump can vary. For example, when used with -A operator, it prints out each packet in ASCII format. Tcpdump is supported by most Unix-based operating systems, such as Linux, Mac OSX and BSD. The Windows variant of tcpdump is known as WinDump.