The railway is divided into sections for operating and safeworking purposes. The start and end of each section is known in Australia and the US as a Block Point, and in the UK as a Block Section boundary (or simply End of Section). In older times these would have mostly had a signal box, but no longer do with the advent of modern signalling and electronic operating systems. The words "Block Point" or initials "BP" are still widely used to define the location, and in many cases this also defines the limit to which a train may run (or shunt) without a further permission being obtained.
If you think of a city street with traffic lights at every intersection, then each set of lights would represent a block point.