X   -   1. A Nasdaq stock symbol specifying that it is a mutual fund.
2. A symbol used in stock transaction tables found on the internet and in newspapers to indicate that a stock is trading ex-dividends or ex-rights.

XBRL - eXtensible Business Reporting Language   -   A standard that was developed to improve the way in which financial data is communicated, making it easier to compile and share this data. XBRL is a type of XML (extensible markup language), which is a specification that is used for organizing and defining data. XBRL uses tags to identify each piece of financial data, which then allows it to be used programmatically by an XBRL-compatible program.

XD   -   A symbol used to signify that a security is trading ex-dividend.

XDIS   -   A symbol used specifically upon the consolidated tape to indicate a security trading ex-distribution.

XRT   -   A symbol used specifically upon the consolidated tape to indicate a security trading ex-rights.

XW   -   A symbol used to signify that a security is trading ex-warrant.

Xenocurrency   -   A currency that trades in markets outside of its domestic borders. "Xeno" is a prefix meaning foreign or strange.

Xetra DAX  -   An all-electronic trading system based in Frankfurt, Germany. Launched in 1997 and operated by the Deutsche Börse, the Xetra platform offers increased flexibility for seeing order depth within the markets and offers trading in stocks, funds, bonds, warrants and commodities contracts.
The Xetra system was originally created for use on the Frankfurt Stock Exchange, but has expanded to be used by various stock exchanges throughout Europe.