GNU sed is the Free Software Foundation's version of the sed(1) editor.

GNU sed isn't really a true text editor or text processor. Instead, it
is used to filter text, i.e., it takes text input and performs some
operation (or set of operations) on it and outputs the modified text.
Sed is typically used for extracting part of a file using pattern
matching or substituting multiple occurrences of a string within a file.

The sed binary is prefixed with the letter g to differentiate it from
the standard application with the same name.