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SECTION 2. DEFINITIONS, ACRONYMS, AND SYMBOLS

ASCII space The ASCII character for space which is represented by decimal 32 (hex-

adecimal 20).

ASCII text The restricted set of ASCII characters decimal 32 through 126 (hexadec-

imal 20 through 7E).

Basic FITS The FITS structure consisting of the primary header followed by a single

primary data array. This is also known as Single Image FITS (SIF), as opposed to

Multi-Extension FITS (MEF) files that contain one or more extensions following

the primary HDU.

Big endian The numerical data format used in FITS files in which the most signifi-

cant byte of the value is stored first followed by the remaining bytes in order of

significance.

Bit A single binary digit.

Byte An ordered sequence of eight consecutive bits treated as a single entity.

Card image An obsolete term for an 80-character keyword record derived from the 80

column punched computer cards that were prevalent in the 1960s and 1970s.

Character string A sequence of 1 or more of the restricted set of ASCII text charac-

ters, decimal 32 through 126 (hexadecimal 20 through 7E).

Conforming extension An extension whose keywords and organization adhere to the

requirements for conforming extensions defined in §3.4.1 of this standard.

Data block A 2880-byte FITS block containing data described by the keywords in the

associated header of that HDU.

Deprecate To express disapproval of. This term is used to refer to obsolete structures

that should not be used in new FITS files but which shall remain valid indefinitely.

Entry A single value in an ASCII table or binary table standard extension.

Extension A FITS HDU appearing after the primary HDU in a FITS file.

Extension type name The value of the XTENSION keyword, used to identify the type

of the extension.

Field A component of a larger entity, such as a keyword record or a row of an ASCII

table or binary table standard extension. A field in a table extension row consists

of a set of zero or more table entries collectively described by a single format.

File A sequence of one or more records terminated by an end-of-file indicator appro-

priate to the medium.

FITS Standard