A so-called market holiday is any non-weekend day when financial markets (New York Stock Exchange, Nasdaq etc) close for the day. On some holidays, the stock markets remain open, while bond markets stay closed or close early.   

Markets can also close due to political events, such as an election or the mourning of a passing president. If the holiday happens to take place on Saturday, the Friday before it typically becomes a stock market holiday. Similarly, markets typically close on the following Monday if the holiday lands on a Sunday.