If you mean the left costophrenic angle:

However, this is a photo of an X-ray film with glare and limited detail, so a reliable report needs the original digital chest X-ray and clinical context. Blunting of a costophrenic angle can suggest pleural fluid, but it cannot be confidently confirmed or excluded from this photograph alone. Murray & Nadel's Textbook of Respiratory Medicine notes that larger pleural fluid collections blunt the lateral costophrenic angle on frontal radiographs.

A blunted costophrenic angle is an X-ray finding at the lower outer corner of a lung, where the diaphragm meets the chest wall.

Normally this corner looks sharp and pointed. “Blunted” means it looks rounded, hazy, or filled in instead.

The most common reason is a small amount of fluid around the lung, called a pleural effusion. Fluid collects in the pleural space and obscures that sharp angle. This may occur with infections such as pneumonia or tuberculosis, heart failure, kidney/liver disease, inflammation, cancer, or after trauma. The X-ray alone cannot identify the cause of the fluid. Radiology teaching case

Other, less common explanations include pleural thickening or scarring, previous infection or surgery, or occasionally positioning/technical factors on the X-ray.

A chest X-ray is usually the first test, but chest ultrasound is often better for confirming a small pleural effusion and estimating its amount. The textbook finding is that blunting of the lateral costophrenic angle is an early sign of pleural effusion on an upright chest radiograph. Roberts and Hedges’ Clinical Procedures in Emergency, Chest Radiograph section.

Seek urgent medical care if this is accompanied by severe shortness of breath, chest pain, bluish lips, high fever, confusion, or coughing blood.