The \addcontentsline command adds an entry to the specified list or table where

• file is the extension of the file on which information is to be written: toc (table of contents), lof (list of figures), or lot (list of tables).
• sec_unit controls the formatting of the entry. It should be one of the following, depending upon the value of the file argument:
• toc the name of the sectional unit, such as part or subsection.
• lof figure
• lot table
• entry is the text of the entry.