The term is sometimes used quite loosely, to mean files that contain only “readable” content (or just files with nothing that the speaker does not prefer). For example, that could exclude any indication of fonts or layout (such as markup, markdown, or even tabs); characters such as curly quotes, non-breaking spaces, soft hyphens, em dashes, and/or ligatures; or other things.

In principle, plain text can be in any encoding, but occasionally the term is taken to imply ASCII. As Unicode-based encodings such as UTF-8 and UTF-16 become more common, that usage may be shrinking.

Plain text is also sometimes used only to exclude “binary” files: those in which at least some parts of the file cannot be correctly interpreted via the character encoding in effect. For example, a file or string consisting of “hello” (in any encoding), following by 4 bytes that express a binary integer that is not a character, is a binary file. Converting a plain text file to a different character encoding does not change the meaning of the text, as long as the correct character encoding is used. However, converting a binary file to a different format may alter the interpretation of the non-textual data.