Secondary hypertension is defined as high blood pressure resulting from an identifiable underlying condition, such as kidney disease, hormonal disorders, or vascular issues. Unlike primary hypertension, which accounts for the majority of cases, secondary hypertension is less common and can often be reversible if the underlying cause is effectively treated. Key indicators for diagnosis include severe or resistant hypertension, sudden increases in blood pressure, and cases in younger individuals (under 30 years). Common causes include renal parenchymal diseases, endocrine disorders like hyperaldosteronism, and obstructive sleep apnea.