P - as part of the tire size designation (e.g., P205/65R15) used to indicate tires intended for services on passenger cars.
LT - as part of the size designation (e.g., LT235/75R15) used to indicate the tires are intended for light truck vehicles.
M&S - letters used to indicate a tire suitable for Mud and Snow and/or All Season usage.
XL - as part of the size designation (e.g., P235/75R16 XL) used to indicate the tire can carry more loads as the maximum inflation pressure and load are greater than a standard load version. (Also could be called REINFORCED or RF).
ZR - as part of the tire size designation (e.g. 225/45ZR17 XL) used to indicate the tire has a maximum speed over 240 kilometer per hour.