A candle whose open and close are nearly equal, showing indecision between buyers and sellers.
The parts of a candlestick. One candle sums up a slice of time: the thick real body runs from the opening price to the closing price, and the thin wicks reach out to the highest and lowest prices traded. Colour tells you which way the body ran.
A doji has almost no body and often long wicks in both directions. It says the period ended about where it started despite movement in between.
On its own a doji means very little. After a strong trend, at a known support or resistance level, it can mark a pause that sometimes precedes a reversal. Context does the work, not the shape.
Example: after five straight up days, a stock opens at $80.00, ranges from $78.50 to $81.50, and closes at $80.05. That doji at a prior high is a reason to watch the next candle closely, not a signal by itself.