The term "stop out" is commonly used in finance and investing to describe a situation where an individual or institution is unable to buy or sell additional shares, options, or other securities due to having reached their maximum allowed limit. This can occur when the amount of money they have invested reaches 100% of the value of the security they are purchasing, or if there are no more available shares left for them to purchase at that time.
In some cases, a stop out may also refer to an account being closed due to insufficient funds, or because the balance has fallen below a certain threshold level. This can happen in situations where margin trading is involved, and the trader fails to meet their obligations by making additional payments or securing more funds into the account.
Overall, "to stop out" means that an investor is unable to participate further in a particular transaction due to having reached their maximum allowed limit or because of insufficient funds.