Each disease, type of disorder, or clinical trial can have its own definition of a partial remission.
For example, a partial remission for cancer may be defined as a 50% or greater reduction in the measurable parameters of tumor growth as may be found on physical examination, radiologic study, or by biomarker levels from a blood or urine test.
Relapse is a term to describe returning symptoms of the disease after a period of remission.
In this case it is still possible for the person to be demonstrating some symptoms, but they are at a subclinical severity or frequency that does not merit re-diagnosis.
Signs and symptomsSyndromeDisease Medical diagnosisDifferential diagnosisPrognosis AcuteChronicCure Eponymous diseaseAcronym or abbreviationRemission