The P or LT designation indicates the type of tire. P-metric tires are for passenger vehicles, while LT tires (Light Truck) are for light trucks, vans, and SUVs.
The 265 indicates the width of the tire in millimeters.
The 75 indicates the aspect ratio, or the height of the tire sidewall as a percentage of the width.
The R indicates that the tire is a radial tire.
The 16 indicates the diameter of the wheel that the tire is designed to fit.