ThinkPad W series
The W series was developed as a workstation machine line, which was supposed to be a replacement for the lack of a T500p, T510p, etc. They were also produced with graphics chips that were better than their T series counterparts, which was the only difference that separated them from the T series. Other than that, they were completely identical in appearance and functionality. This excludes the special W70x models, however.
The meaning of the W series would soon make no sense, as the T440p and the T540p co-existed alongside the W540.
Due to the possible confusion between a Txx0p and an actual W5x0, the W series was then discontinued afterwards to prevent that from happening.