Technical Director (also called a TD) is a common job title in computer animation and visual effects companies.  Some companies use the title "TD" for several different jobs:

Lighting TD's (the most popular use of the word) are the artists who light and render 3D scenes.

Character TD's are responsible for rigging a character with a skeleton, clothing, hair, and deformation controls.

Shader TD's write and adjusts shaders to determine the appearance of models, and prepare objects to be painted by the texture painters.

Effects TD's......

At some companies, TD's are sometimes doing modeling work in earlier stages of a production, are involved in compositing and effects animation, or "Pipeline TD's" are involved in developing the architecture that links all of the departments together.  Despite all these different meanings of TD, if someone doesn't specify what kind of TD they are, then they are usually working on lighting and rendering.

How "Technical" are TD's?

TD positions require a balance of artistic sensibilities, technical savvy, a good eye, and good problem-solving skills.  A few TD's are programmers, but most are not.  Many TD's know how to write scripts in different scripting languages, such as MEL, Tcl, Perl, or Python.  Almost all TD's are able to work with different operating systems, including being proficient with common UNIX shell commands.  Among the TD's that have scripting or programming skills, most spend their time working on specific characters or shots, and only doing scripting or programming when needed to speed up their work or solve a production problem.  If you want to find where the real, hard-core programmers are working in a larger studio, look at the Programming, Tools, or R&D departments - they are all more "technical" than the TD's.

Are TD's really "Directors?"

The work that many TD's do in lighting and rendering is similar to the work of the "Director of Photography" (or DP) in live-action film production.  Otherwise, the name TD can be a bit misleading, and some studios don't even use the term.  At some companies, the person lighting a shot would be called a Lighting Animator or simply a Lighter, instead of a Lighting TD.  People rigging characters are sometimes called a Rigger, Puppeteer, Physiquer, Technical Animator, or other titles instead of Character TD.  Because of this, some companies will never list a help-wanted ad for TD's.  A TD by any other name is still a TD, though, and they still need to hire people with similar skills for any computer graphics production.