What term is commonly used to describe limits placed on trading during price extremes?

The term "Lock Limit Up" is used to describe the practice wherein trading limits are imposed when a security reaches a price extreme, often during periods of excessive volatility. This mechanism is designed to prevent prices from moving too far in one direction too quickly, which can be destabilizing for the market. By instituting a lock limit, exchanges can pause trading for a period, allowing for a cooling-off period where investors can reassess the situation and trades can be executed at more reasonable prices.

In contrast, other terms may refer to different concepts. A price cap typically refers to a maximum price level that allows for trading but does not encompass the broader implications of volatility or extreme price movements. A trading halt serves a similar purpose but usually occurs in response to specific news or events rather than price extremes alone. Market boundary is not a widely recognized term in this context and does not specifically convey the idea of limits imposed due to price fluctuations.

Thus, "Lock Limit Up" accurately captures the specific mechanism in trading that addresses volatility and helps maintain market stability.