Edge Stability Simple explanation: Ability to hold a fine, acute, polished edge.
In depth: Edge stability is controlled most by carbide size and volume. The finer the carbide structure, the better a steel is at holding sharpness when sharpened very acutely and at a high polish. Evidences of a steel with low edge stability are losing initial sharpness quickly or chipping either while cutting or while sharpening with an acute bevel. The finer the edge and the finer the polish the more this will be apparent. Edge stability and toughness are often connected, but not always the same. Sometimes a steel can have high edge stability with fairly low toughness, or a steel with low edge stability can have moderate toughness. Blue Super has fairly high edge stability but low toughness; D2 has low edge stability but moderate toughness. Generally wear resistance and edge stability are opposed to each other since a greater volume of carbides means greater wear resistance but less toughness and edge stability, meaning one of the most important factors for selecting a steel are how much slicing it will be doing and how thick the edge will be. As already said, usually edge stability is more important in kitchen knives.