aux

Aux is an abbreviation of auxiliary, used in computing and technology to denote something that supports a primary function, such as auxiliary data, devices, or inputs. The exact meaning is contextual; common uses include auxiliary files, auxiliary power, and auxiliary input or output.

In TeX and LaTeX, the file with the .aux extension is an auxiliary file created during compilation. It stores cross-reference information such as labels, page numbers for references, and entries for the table of contents, list of figures, and lists of tables. The .aux file is read by subsequent runs to resolve references and to help BibTeX or biber generate bibliographies. It is a plain text file named after the main document (for example, mydocument.aux) and is typically located in the same directory as the source. Deleting the file forces a full re-run, which can temporarily delay reference resolution until new data is written.

In DOS and Windows systems, AUX is a reserved device name that refers to the system console for input and output. It belongs to a set of reserved names such as CON, NUL, PRN, and cannot be used for regular file names in many contexts. Input or output redirection to AUX interacts with the console rather than a file on disk.

As a prefix, aux- appears in many terms to denote supplementary components such as auxiliary power, auxiliary input, or auxiliary verb in linguistics. The term is also used in various technical domains to label secondary or supporting systems and data.