"100/40" typically refers to a blood pressure reading, where the first number (100) represents systolic pressure and the second number (40) represents diastolic pressure. Systolic pressure measures the force of blood against artery walls when the heart beats, while diastolic pressure measures that force when the heart is at rest between beats. A reading of 100/40 is considered low blood pressure, or hypotension. This condition can lead to symptoms such as dizziness, fainting, or fatigue. It is important for individuals with low blood pressure to consult a healthcare professional for proper evaluation and management.