If you look in the source code directory ($lazarusdir$\components\tachart):
-the readme.txt file indicates a "LGPL component", but
-all the source code files have this header:
*****************************************************************************
See the file COPYING.modifiedLGPL.txt, included in this distribution,
for details about the license.
*****************************************************************************
Authors: Alexander Klenin
So, I'd said that it's clear for me that TaChart has exactly the same license as the rest of the "general" LCL : modifiedLGPL.txt
Which means that you can use it in any kind of programs: open or closed source, free or commercial.
But, if you modify the TaChart source code, and if you release your program publicly (i.e. not for yourself of for your company only), you must also release your modifications publicly, under the same license.
**Addition** The (main ?) package tachartlazaruspkg.lpk indicates also a modifiedLGPL license.
The readme.txt file (i.e. 2008) and the wiki documentation are probably outdated.
.