- ANSI: American National Standards Institute. FITS standard often refers to ANSI definitions and standards.
- ASCII: American Standard Code for Information Interchange. FITS headers use a subset of ASCII characters.
- ASCII character: Any member of the seven-bit ASCII character set. FITS records must use only ASCII characters.
- CCD: Charged-Coupled Device is the most widely used electronic sensor used in astronomy to produce digital images. CCD is an integrated circuit based on an array of coupled (or linked) capacitors. Each capacitor is able to transfer its electric charge to a neighbouring capacitor. A series of such transfers leads to a complete readout of the array and by interpreting the readout the digital image is generated.
- FITS: Flexible Image Transport System
- FORTRAN: (derived from Formula Translation) is a general-purpose programming language well suited for numeric, scientific, and engineering applications developed by IBM in the 1950s and widely used until the 1990s. FITS headers and their organisation in records and keywords, as well as many of the data types and formats, closely resemble those of the FORTRAN language.
- MEF: (Multi-Extension FITS). FITS file containing a primary HDU followed by one or more extension HDUs. An example of such file could be an image taken with different filters, all combined into the same FITS file.
- SIF: (Single Image FITS). FITS file containing only a primary HDU and without any extension HDUs or Special Records. Historically, this is known as the Basic FITS.
- SWIFT: A modern, general-purpose programming language developed by Apple and announced in June, 2014. Swift's powerful
enum type is especially well suited for developing a parser for interpreting FITS headers (records, keywords). Currently, Swift is the primary language for new development for all Apple devices, but Swift compilers exist for almost any other platform as well.