The endpoint adjoining the square bracket is known as "closed", while the endpoint adjoining the parenthesis is known as "open". If both types of brackets are the same, the entire interval may be referred to as "closed" or "open" as appropriate. Whenever infinity or negative infinity is used as an endpoint (in the case of intervals on the real number line), it is always considered "open" and adjoined to a parenthesis. The endpoint can be closed when considering intervals on the extended real number line.