GNU Emacs Manual
K.7 Replacement Commands
Global search-and-replace operations are not needed often in Emacs,
but they are available. In addition to the simple M-x
replace-string command which is like that found in most editors,
there is a M-x query-replace command which finds each occurrence
of the pattern and asks you whether to replace it.
The replace commands normally operate on the text from point to the
end of the buffer; however, in Transient Mark mode, when the mark is
active, they operate on the region. The replace commands all replace
one string (or regexp) with one replacement string. It is possible to
perform several replacements in parallel using the command
expand-region-abbrevs (see section X.3 Controlling Abbrev Expansion).