T4, T5, T6, IW5 - What do they all mean?#

In short, these refer to the codename each game is based off of during it's development.

They are as follows:

• T4 - World at War
• T5 - Black Ops I
• T6 - Black Ops II
• IW5 - Modern Warfare 3

They are based on who developed the game and which game number it was for that studio. T4 was Treyarch's 4th Call Of Duty game and IW5 was Infinity Ward's fifth, for example.