A "default" is the failure to perform a legal obligation. For example, a mortgage or deed of trust is said to be in default when the borrower fails to make a required monthly payment. A default can lead to severe legal consequences, such as a foreclosure of a property by a mortgage lender if the borrower has defaulted.
"Ticker symbols" are the letters or characters used as a code to identify publicly traded stocks or mutual funds. The number of characters can identify the exchange on which the security is traded and provide other information about that security. For example, NASDAQ stocks are typically identified by four characters, such as MSFT for Microsoft. Symbols with five letters ending in X are used for mutual funds.