For space truss, the upper chord and the lower chord refer to the upper and lower horizontal members, and the web member is the diagonal member in the middle.
The upper part of the diagram is a plan view of the grid, and the lower part is a front view of the grid. In the figure, the yellow component is the top chord of the grid, the blue component is the web component, and the green component is the bottom chord of the grid.
I hope it helps you.