A mixture of characters within a text, where some are read from left to right and others from right to left. Bidirectional or bidi refers to an application which allows for this variance.

A mixture of characters that are read from left to right and characters that are read from right to left. Most Arabic and Hebrew characters, for example, are read from right to left, but numbers and quoted Western terms within Arabic or Hebrew text are read from left to right.

Properly speaking, ''bidirectional text'' is text containing both left-to-right and right-to left portions. The term is also sometimes loosely applied to pure right-to-left text. All right-to-left text requires using the bidirectional stack, because the default embedding level of zero implies left-to-right text.