Overview
A long full candle is one that has a long stick, and a body that fills most of the stick (full).
Interpretation
The price action was strong and in one direction during the day. If the candle is bullish (green), it means that the price started at the open and continued in a near linear fashion up to the close, without showing much weakness.
A sample realization
In Context
If the candle appears during a trend, and moves in the direction of the trend, it confirms the trend. If the candle is accompanied by strong volume, the indication is a strong confirmation in the direction of the candle.
Long full candles can be followed by a bit of retracement, profit taking and mean reversion in the short term, but may be an indicator of the longer term direction.