What is "strez"

Strez (; original spelling: СТРѢЗЪ) ( fl. 1207–1214) was a Bulgarian sebastokrator and a member of the Asen dynasty. A major contender for the Bulgarian throne, Strez initially opposed the ascension of his close relative Tsar Boril. He fled to Serbia, where he accepted the vassalage of Grand Prince Stefan Nemanjić, and Serbian support helped him establish himself as a largely independent ruler in a large part of the region of Macedonia. However, Strez turned against his suzerains to become a Bulgarian vassal and joined forces with his former enemy Boril against the Latins and then the Serbs. Strez was murdered amidst a major anti-Serbian campaign under unclear circumstances in a plot that likely involved Saint Sava.