[rich_sasha]

I thought T refers to overgrown top management and a long tail of managers managing other managers. And one guy at the bottom doing all the typing.

[UweSchmidt]

Scrum master, Business Analyst, misc devs and QA contribute marginally and hope that one developer who groks the entire thing gets something done.

[polotics]

Developers add cleverness until only themselves grok the accidental complexity, QA and BA's develop the actually useful bits on the side, the developers quit to implement more Cloud at the next startup. Introducing the Q shaped model...

[sigg3]

And then there's the "lone genius" who is doing everything in order to prevent anyone else from contributing.

[jimmySixDOF]

T shapes are used also for building teams so you think about an overlap of people who understand at a high level what others are doing but still emphasize the individual specialization of subject matter experts. It's like Tetris but for teams.