A Renko chart adds a brick only when price travels a chosen distance from the last brick, typically the brick size or twice it in the opposite direction. Time is ignored, so an hour of chop may print nothing while a fast move prints ten bricks.
Example: with a $1 brick on a stock at $50, a rise to $51 prints one green brick. A fall to $49 then requires a $2 move, printing two red bricks. This asymmetry is what filters noise.
Renko is useful for seeing trend persistence and for stripping out sideways chop. Its weaknesses are serious: the last brick can repaint until confirmed on some platforms, the chart hides how long a move took, and brick size is a free parameter that is easy to curve-fit (see overfitting). Sizing bricks by atr is more honest than picking a round number that looks good on history.
Related: kagi-chart, point-and-figure, range-bars, heikin-ashi