Grandmaster was a title awarded to individuals who were exceptional players of games such as chess and strategema.
The Zakdorn Sirna Kolrami was a third level grand master in strategema. William T. Riker believed it an honor to even play someone of such stature. (TNG: "Peak Performance")
When he needed to reduce the size of his holoprogram for transmission to Jupiter Station in 2376, The Doctor told Seven of Nine she could remove his grand master chess program. (VOY: "Life Line")
In 2381, a six-year-old Zakdorn became the youngest player ever to be crowned Strategema Grandmaster. (LD: "Grounded")
According to his dossier at the official Star Trek movie website, in the alternate reality Spock was awarded the title "Grandmaster" by the Federation's Three-Dimensional Chess Organization. (β)