In a Parliamentary election conducted under a non-proportional electoral system, some districts or constituencies are held with smaller majorities than others. These seats require a smaller swing to change hands and are therefore typically the focus of most of the parties' campaign resources. The concentration of money and manpower to areas where they will make the most difference is known as targeting.
A similar phenomenon happens in US Presidential elections, where the electoral college system means that candidates must win states rather than votes. Again, resources are concentrated towards the swing states with the smallest majorities.
