When it comes to describing the phrase "open end," there are several synonyms that can be used depending on the context. One possibility is "unlimited," which indicates that there are no specific boundaries or restrictions in place. Another potential synonym is "indefinite," which suggests a lack of fixed endpoint or schedule. Alternatively, "flexible" might be used to convey the idea of adaptable or responsive to changing circumstances. "Non-specific" is another option which implies a broadness or lack of detail, while "unbounded" or "unrestricted" focus more on the absence of limitations. Ultimately, the choice of synonym will depend on the specific tone or emphasis that the writer is trying to convey.