Nodes
The points of the domain where the function is known or evaluated.
Definition
In interpolation they are the points the polynomial passes through; in quadrature, the abscissas where the integrand is evaluated. Their number and placement (equispaced, Chebyshev, Gauss) determine the achievable accuracy.
How it is used
With tabulated data the nodes are given; when you can choose them, placing them well (Gauss, Chebyshev) buys extra orders of accuracy.