BSL, or Blood Sugar Level, refers to the concentration of glucose in the bloodstream, typically measured in millimoles per litre (mmol/L). Monitoring BSL is crucial in managing diabetes, as abnormal levels can lead to acute complications such as hypoglycaemia or hyperglycaemia, which may result in serious health issues if not addressed promptly. Regular assessment of BSL helps guide treatment decisions and optimise glycaemic control in patients.