Transparent represents perfect transparency in graphics or style specifications.
Underoverscript[x, y, z] is an object that formats as x_y^z.
WordSeparators is an option for Read, Find, and related functions that specifies the list of strings to be taken as delimiters for words.
$Language is a list of strings which give the names of languages to use for messages.
In some cases you may need to specify pattern sequences that are more intricate than things like x__ or x..; for such situations you can use PatternSequence[p_1,p_2,…]. ...
NB
(Mathematica Import/Export Format) Registered MIME types: application/mathematica, application/vnd.wolfram.mathematica Mathematica notebooks. Used for storing and exchanging Mathematica input and output and ...
Package
(Mathematica Import/Export Format) Registered MIME type: application/vnd.wolfram.mathematica.package Mathematica package source format. Used for storing and exchanging Mathematica programs, packages, and data. ...
SCT
(Mathematica Import/Export Format) Scitex CT format. Raster image file format. Used for pre-press imaging applications. SCT is an acronym for Scitex Continuous Tone. Binary format. Stores images as RGB, CMYK, ...
SHP
(Mathematica Import/Export Format) ESRI shape file format. Common GIS file format. Used for archiving and exchanging cartographic and geospatial information. Stores the geometry and data of map features. SHP ...
ZPR
(Mathematica Import/Export Format) ZPrint CAD format. Used with Z Corporation 3D printers. Native format of the ZEdit and ZPrint applications. Developed by Z Corporation. Stores a physical 3D model and color ...