Loss of lumber lordosis is seen" what does actually mean. is this a serious problem?

No: Was this on an x-ray report? It just means that the curve in your lower back is less than usual. By itself it is not meaningful finding. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine, if you are under 27 years of age.

Structural change: The axial,spine has curves to allow better motion. If those curves change (scoliosis is a side to side curved, kyphosis is a curve away from the navel , lordosis is a curve toward the navel and loss of lordosis means the alignment of the lower spine is now straight. This generally is associated with muscle spasm and degeneration. Physical therapy, chiropractic, exercises can help. Not serious.