what is ert
The acronym ERT (Evil Red Text) refers to raw LaTeX commands inserted into the body of your LyX document. In historical versions of LyX, ERT appeared in the user interface alongside regular text as red characters. ERT was coined on the developers mailing list by Larry Marso, who advocated an embedded raw LaTeX inset to hide raw LaTeX, and thus, to present a cleaner LyX user interface for complex documents. (see A Brief History of ERT, LDN, March 15, 2000).