A delimiter is a character (or contiguous set of characters) used to separate pieces of data within a file or to designate the beginning or end of a programming construct. Without delimiters the interpretation of a stream of data would be more complex.

The programming language or operating system usually dictates the characters used as delimiters. Programming languages use a variety of delimiters to indicate comment information and special processing requirements. Command line usage of delimiters commonly includes the backward slash (\) and forward slash (/). Data files commonly use commas, semicolons, or tabs as delimiters.

Additionally delimiters are used both as separators between individual data fields and as terminators at the end of a data file. To avoid confusion these field-level and file-level delimiters must be different characters, and they must not appear within the data itself. The program processing the data file must understand how to process each delimiter in order to interpret the contents of the data file.