Definition of "metacharacter"

This chapter moves on to look at several regular expression metacharacters and modifiers. Metacharacters can be combined with literal characters and quantifiers, which were discussed in Chapter 3, to create more complex regular expression patterns.

2005, Andrew Watt, Beginning Regular Expressions, John Wiley & Sons, page 73

You can't enter invisible characters—such as tab characters, line-end characters, or carriage returns—in the Find What or Change To fields. To get around this, you enter codes—known as “metacharacters”—representing those characters.]

[2006, Olav Martin Kvern, David Blatner, Real World Adobe InDesign CS2, Peachpit Press, page 224