The characteristics of nephrotic syndrome are defined by significant proteinuria, where significant proteinuria refers to urinary protein exceeding 3.5 grams in 24 hours; hypoproteinemia, which refers to blood albumin levels below 30 grams per liter; edema, which may present in facial and lower limbs, and even severe patients may exhibit generalized edema around both lower limbs; and hyperlipidemia, characterized by increased cholesterol and triglycerides in the blood. These patients may exhibit reduced urine output, edema, and noticeably increased foam in the urine.