An Acronym for Stream EDitor
A very simple ProgrammingLanguage geared towards text manipulation for files larger than the avaliable RAM. SED scripts are very hard to read if they try to do anything even moderatly complex; you're better of using AWK or Perl in such cases. The latter has copied many concepts from both of the former languages.
See also:
CategoryProgrammingLanguages, CategorySpecialPurposeProgrammingLanguages
5 pages link to SED: