Chest xray: there is a tiny left effusion & there is mild retrocardiac ill defined opacity. left lung. explain?

See answer: you have some fluid (effusion) in your lung and a type of unknown and not particularly known (ill defined) mass (opacity) behind your heart area (retrocardiac). These findings are not normal and they need to be followed up asap with an examination and further diagnostic testing as well. Seeing a Pulmonologist (Lung specialist) is advisable. Best wishes.

Explanation: Effusion means in simple terms a collection of fluid. An opacity is an area that shows up on the xray which is not the same density as your lung itself and therefore is not normally there. They stated ill defined, so they may likely go further with a CT scan. The effusion may be related to the opacity. More than this is difficult to say without more information.