Error bars are a visual representation of the uncertainty or variability in a set of data. They are commonly used in graphs and charts to show the range within which the true value of an unknown quantity lies with a certain degree of confidence.
The error bars can take different forms depending on the type of data being presented, but they generally indicate two values - one that represents the lowest possible value (usually based on some form of statistical analysis) and another that represents the highest possible value (also based on statistical analysis). These two values are then plotted on either side of the central value or average of the dataset.
In essence, error bars provide important context for interpreting data by showing how much uncertainty there is in the measurements being presented. This can help readers to better understand the limitations and potential variability within a set of results, allowing them to make more informed decisions based on that information.