  Robust and comprehensive characterization of the topological properties of
complex networks requires the adoption of several respective measurements,
among which the node degree has special importance. In the present work, we
provide an introduction to one of these measurements, namely the accessibility
of a node, which can be understood as a generalization of the concept of node
degree not only to incorporate successive neighborhoods of that node, but also
to reflect specific types of dynamics unfolding in the network. After
discussing the node degree and its hierarchical extension, we present the
concepts of random walk, entropy, and then the accessibility. Several examples
of its numeric calculation are provided, as well as some experimental results
indicating that it can effectively complement the information provided by other
topological measurements of four types of complex networks, namely Erdos-Renyi,
Watts-Strogatz, Barabasi-Albert, and Geometric. We also describe how a recently
developed toolbox can be used for the calculation of accessibility in
relatively large networks.
