adj. Having skills and knowledge that are both deep and broad.
However, the speed with which media agencies (and clients) have embraced communications planning has caused concern. For it to really work, communications planners need to be "T-shaped" people. … "T-shaped" communications planners, with a background in media, have a deep understanding of media, and a broad understanding of the other disciplines within the marketing spectrum. They might not have a deep understanding of the minutiae of direct marketing, but they would broadly understand the repercussions of its inclusion in a through-the-line campaign.

To continue the alphabetical analogy, if the ideal communications planner is "T-shaped", then a classic media agency employee is "I-shaped" — with a deep understanding of their discipline, but not necessarily of any other — and a classic client-side employee "hyphen-shaped", their role requiring a broad understanding of many disciplines rather than specific knowledge of one. The worry is that media agencies are trying to do a "T" job with "I" people.
—Angus Bannerman, “Want to plan campaigns? Best get your 'I's crossed,” Marketing Week, October 02, 2003
Training scientists is fundamental to the growth of the field, participants said. Jelinski, who is vice chancellor for research and graduate studies at Louisiana State University, talked about a new "T-shaped" person with disciplinary depth, in biology for example, but with the ability, or arms, to reach out to other disciplines. "We need to encourage this new breed of scientist," she said.
—Dave Amber, “Researchers Seek Basics Of Nano Scale,” The Scientist, August 21, 2000
1991 (earliest)
The hunt for a new breed of computer manager is on. The British Computer Society, in a controversial report published last year, described the quarry as a ''hybrid'' manager who would combine business expertise with IT skills. The hybrid manager, it said, would be distinguished by his or her ability to relate to ''the broad picture'' and to people, understanding their motivation and aspirations; he or she would also be energetic, intuitive, a good listener, and (cryptically) would have ''an unusual set of interests''.

This type of rounded personality is also sought in other branches of the same theory, which prizes individuals known as T-shaped People. These are a variation on Renaissance Man, equally comfortable with information systems, modern management techniques and the 12-tone scale.
—David Guest, “The hunt is on for the Renaissance Man of computing,” The Independent (London), September 17, 1991