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indentation in·den·ta·tion (ĭn'děn-tā'shən)
A notch, a pit, or a depression.
A space left between the left-hand margin of a line of type or handwriting and the beginning of a sentence or quotation. The beginning of a paragraph is usually indented.
document, text, programming
Space and/or tab characters added at the beginning of one or more consecutive lines to indicate the structure of a piece of text, e.g. indenting a passage to make it stand out.
Indentation is important in source code for readability. See indent style. Some programming languages go further and use indentation as the main method to represent block structure to the compiler or interpreter, see off-side rule.