What is meant by loop?

A loop is a collection of nodes in a flow graph such that
i)    All nodes in the collection are strongly connected i.e., from any node in the loop to any other, there is a path of length one or more, wholly within the loop
ii)    The collection of nodes has a unique entry, i.e. a node in the loop such that the only way to reach a node of the loop from a node outside the loop is to first go through the entry.