Consensus forecast
The consensus is economists' average forecast for an upcoming data release. The market mostly reacts to the gap with the published figure.
Before each release, economists polled by news agencies give their estimate. The median of those forecasts forms the consensus shown in the economic calendar.
Prices already reflect that consensus. A figure in line with expectations barely moves the market. A clear surprise, either way, triggers the move. That is why a “good” number can push a currency lower if it is worse than expected.
The market sometimes has an unofficial expectation, the “whisper number”, that differs from the official consensus, shaped by other indicators released earlier. It explains some puzzling reactions.