The short day candlestick pattern (view full size chart) is one of the single candlestick patterns (i.e. it consists of only one candlestick), and by itself it is neither a bullish nor bearish pattern (as it consists of both bullish and bearish trading).
The short day candlestick opens and closes inside of the previous candlestick's range (i.e. between its high low), and is completely contained by the previous candlestick. The short day pattern is neither bullish nor bearish, regardless of whether the time frame consisted of primarily bullish or bearish trading.
Note that the short day candlestick pattern is so named because it has a short candlestick length (i.e. a small range), not because it is associated with a short trade.
Use In Trading
The short day pattern can occur in a number of different contexts (e.g. at the beginning of a trend, during a trend, at the end of a trend, etc.), and by itself it only indicates that the time frame was neither bullish or bearish, and had a small range. Therefore, the short day is not often used as an trade entry or exit pattern. The short day is also included in some of the two or three candlestick patterns, in which case it has more relevance, and can provide an indication of upcoming price movement.
