A node of a polygon. Minimum is 3 vertexes/vertices for each polygon in a level (otherwise the edges between the vertexes couldn't form a polygon). Limit of polygons in Elma demo version was 5 and limit of vertexes was 10 per polygon. In full version the limits are 300 polygons and 1000 vertices. Not to be confused with edge, though a polygon always has same amount of vertices (nodes, corners) and edges (arcs, lines).
Vertical synchronization. Switching vsync on you can limit the frame rate to your screen's refresh rate. If you don't know whether you have vsync on or off, it's probably on. See Refresh Rate and Tweaking page for more material.