This is relevant for trading in TWTR however it is rarely used even though thresholds are met.
A case of arbitrary rules enforcement.
These are also known as trading curbs or collars. The cap is a general description of them Each exchange has it's own set of rules that govern this.
Only posted to show there are rules on the books.
Single-Stock Circuit Breakers
Unlike their market-wide counterparts, single-stock curbs go into effect whether the price moves up or down. Also note that other exchange-traded products, such as ETFs , fall under the "single-stock" umbrella, making the commonly used name for the rule slightly misleading. Since October 2013, the SEC has used a "limit-up limit-down" mechanism to determine the thresholds for acceptable trading. Halts are triggered by up-or-down moves outside of certain bands, determined based on the security's price and listing:
see cap
https://www.investopedia.com/terms/c/circuitbreaker.asp