LaTeX is a typesetting system, so usually you use it together with an editor and a viewer. TeXmacs is one program which does it all in such a way that you can edit the typeset document directly and that what you see on the screen is exactly what will be on the final PDF. These features make it unique. Typesetting quality is comparable to TeX in the sense that you can well mistake a TeXmacs document with a LaTeX one. TeXmacs has an integrated picture editor and a presentation mode, and you can have interactive sessions in your document e.g. with software like R, Python, Scheme, Axiom, Reduce, etc... Actually you can even run code inside TeXmacs to produce images with libraries like TikZ/FeynMF/DraTeX/Asymptote/Graphviz whose functionalities have no equivalent (yet) in TeXmacs.
Since he seems to have used it already I also assumed (s)he knew the difference and that with TeX it was meaning a TeX-based workflow. But I wanted to make clear the difference for newcomers since TeXmacs is often misinterpreted as just a TeX frontend, which is not the case.
