C[0,0] refers to the set of continuous functions defined on the closed interval [0, 0]. Since this interval contains only a single point, the only function in C[0,0] is the constant function that takes the value at that point. In mathematical terms, C[0,0] can be seen as a space of functions where every function is continuous and defined at the point 0. This concept is often used in functional analysis and topology, where the properties of functions are studied in relation to their continuity and limits.