Kashida

Kashida (Persian: کشیده‎‎; "extended", "stretched", "lengthened") is a type of justification used in some cursive scripts related to Arabic. In contrast to white-space justification, which increases the length of a line of text by expanding spaces between words or individual letters, kashida justification is accomplished by elongating characters at certain chosen points. Kashida justification can be combined with white-space justification to various extents.

The analog in European (Latin-based) typography (expanding or contracting letters to improve spacing) is sometimes called expansion, and falls within microtypography. Kashida is considerably easier and more flexible, however, because Arabic-Persian scripts feature prominent horizontal strokes, whose lengths are accordingly flexible.

For example, alħamdu and Raḥīm with and without kashida may look like the following:

Kashida can also refer to a character representing this elongation (ـ) – also known as tatweel or taṭwīl (تطويل taṭwīl) – or to one of a set of glyphs of varying lengths that are used to implement this elongation in a font. The Unicode standard assigns codepoint U+0640 as "Arabic Tatweel".

The kashida can take a subtle downward curvature in some calligraphic styles and handwriting. However, the curvilinear stroke is not feasible for most basic fonts, which merely use a completely flat underscore-like stroke for kashida.

In addition to letter spacing and justification, kashida is also used for emphasis and as book or chapter titles. In modern Arabic mathematical notation, kashida is found in some operation symbols that need to be stretched to accommodate associated contents above or below them.

...
Wikipedia