Analysts at banks and research firms publish estimates for a company's future revenue and earnings per share. Data providers collect these and report an average or median, often called the consensus estimate. When a company reports results, the market compares them with that figure to decide whether it beat, met or missed expectations.
It is a useful reference because stock prices tend to move on surprises relative to expectations, not on the numbers alone. A company can report record profit and still fall if the result is below consensus.
It has weaknesses. Analysts tend to follow each other, estimates can be stale, and the figure differs by provider. Analysts may also have conflicts of interest, and consensus has often been wrong during sudden changes.
Check how many analysts contribute, see the range and not just the average, and treat consensus as a benchmark and not as a prediction.