Anchoring bias describes the cognitive error you make when you tend to give more weight to information arriving early in a situation compared to information arriving later ― regardless of the relative quality or relevance of that initial information.
Whatever data is presented to you first when you start to look at a situation can form an "anchor" and it becomes significantly more challenging to alter your mental course away from this anchor than it logically should be.
A classic example of anchoring bias in emergency medicine is "triage bias," where whatever the first impression you develop, or are given, about a patient tends to influence all subsequent providers seeing that patient.
For example, imagine two patients presenting for emergency care with aching jaw pain that occasionally extends down to their chest. Differences in how the intake providers label the chart ― "jaw pain" vs. "chest pain," for example ― create anchors that might result in significant differences in how the patients are treated.