What exactly do we mean by bias?

" Colloquially speaking, bias is defined as a prejudice for or against one person or group, typically in a way considered to be unfair. Bias in the machine learning sense is defined a bit differently, as an “error from erroneous assumptions in a learning algorithm.” In other words, a model consistently making the same mistakes."

A visualization of bias in machine learning as darts on a dartboard — the model’s predictions are consistent but skewed.