A text file (sometimes spelled "textfile") is a kind of computer file that is structured as a sequence of lines. 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.
"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.
At a generic level of description, there are two kinds of computer files: text files and binary files.
The ASCII character set is the most common format for English-language text files, and is generally assumed to be the default file format in many situations. For accented and other non-ASCII characters, it is necessary to choose a character encoding. In many systems, this is chosen on the basis of the default locale setting on the computer it is read on. Common character encodings include ISO 8859-1 for many European languages.
Because many encodings have only a limited repertoire of characters, they are often only usable to represent text in a limited subset of human languages. Unicode is an attempt to create a common standard for representing all known languages, and most known character sets are subsets of the very large Unicode character set. Although there are multiple character encodings available for Unicode, the most common is UTF-8, which has the advantage of being backwards-compatible with ASCII: that is, every ASCII text file is also a UTF-8 text file with identical meaning.
Microsoft MS-DOS and Windows use a common text file format, with each line of text separated by a two character combination: CR and LF, which have ASCII codes 13 and 10. It is common for the last line of text not to be terminated with a CR-LF marker, and many text editors (including Notepad) do not automatically insert one on the last line.
Most Windows text files use a form of ANSI, OEM or Unicode encoding. What Windows terminology calls "ANSI encodings" are usually single-byte ISO-8859 encodings, except for in locales such as Chinese, Japanese and Korean that require double-byte character sets. ANSI encodings were traditionally used as default system locales within Windows, before the transition to Unicode. By contrast, OEM encodings, also known as MS-DOS code pages, were defined by IBM for use in the original IBM PC text mode display system. They typically include graphical and line-drawing characters common in full-screen MS-DOS applications. Newer Windows text files may use a Unicode encoding such as UTF-16LE or UTF-8.
When opened by a text editor human-readable content is presented to the user. This often consists of the file's plain text visible to the user. Depending on the application, control codes may be rendered either as literal instructions acted upon by the editor, or as visible escape characters that can be edited as plain text. Though there may be plain text in a text file, control characters within the file (especially the end-of-file character) can render the plain text unseen by a particular method.