The endpoint of a clinical trial is the measurement (such as change in tumour size) used to decide whether there is a significant difference between different arms of the trial (for example, whether a medicine under study is having a positive effect).
There are different types of endpoints. A binary endpoint is defined by whether an event has occurred or not (for example, the relief of symptoms, or occurrence of disease symptoms). It does not imply a certain magnitude of an effect. It is a Yes/No construct.