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ODT is the word processing document format for text document created using word processors that follow the Open Office Document Format. .ODT is the default document format for the OpenOffice.org Writer.

These can be opened with any OpenOffice-compatible program, including NeoOffice (Mac), AbiWord (Mac & Windows), and KWord (Unix) and can also be imported into Google Docs. ODT files are based on the OpenDocument format (ODF), which became the native format for electronic office documents such as spreadsheets, charts, presentations and word processing documents replacing the OpenOffice.org XML format, for open standards based applications.

Related: What is a Docx file?