The wooden or metal struts that are attached horizontally to the upper section of the mast, on both sides. They widen the angle of the shrouds, and thus provide a better support for the mast. Found on http://www.encyclo.co.uk/local/20645
Also crosstrees. Short horizontal struts extending from the mast to the sides of the boat, changing the upward angle of the shrouds. Found on http://www.sailinglinks.com/glossary.htm