Neighborhood basis

Let \(X\) be a topological space and \(x\in X\). A neighborhood basis at \(x\) is a collection \(\ts{B_j}_{j\in J}\) of open subsets of \(X\) containing \(x\) such that for every neighborhood \(U_x\) of \(x\) there exists \(j\in J\) with \(B_j \subseteq U_x\).