Office Open XML (also informally known as OOXML or Microsoft Open XML) is a zipped, XML-based file format developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents. The format was initially standardized by Ecma (as ECMA-376), and by the ISO and IEC (as ISO/IEC 29500) in later versions.
Starting with Microsoft Office 2007, the Office Open XML file formats have become the default target file format of Microsoft Office. Microsoft Office 2010 provides read support for ECMA-376, read/write support for ISO/IEC 29500 Transitional, and read support for ISO/IEC 29500 Strict.Microsoft Office 2013 and Microsoft Office 2016 additionally support both reading and writing of ISO/IEC.
A text file (sometimes spelled "textfile": an old alternative name is "flatfile") is a kind of computer file that is structured as a sequence of lines of electronic text. A text file exists within a computer file system. The end of a text file is often denoted by placing one or more special characters, known as an end-of-file marker, after the last line in a text file. Such markers were required under the CP/M and MS-DOS operating systems. On modern operating systems such as Windows and Unix-like systems, text files do not contain any special EOF character.
"Text file" refers to a type of container, while plain text refers to a type of content. Text files can contain plain text, but they are not limited to such.