What a marginal seat is
Launch library · evergreen read
A marginal seat is an electorate where the margin between the winning and losing candidates was narrow at the previous election, meaning a relatively small shift in votes could plausibly change which party or candidate wins next time, however small it might initially seem, which is one reason the rules keep evolving.
Because outcomes in these seats are genuinely uncertain, campaigns often direct disproportionate attention and resources toward marginal electorates, since winning or losing there is more likely to influence the overall composition of parliament than a similar effort in a safer seat, a point worth keeping in mind going forward.
Commentators frequently use the number and location of marginal seats as a rough guide to how competitive an upcoming election is likely to be, since a large bloc of marginal seats generally signals a genuinely close overall contest, as most functioning systems eventually demonstrate, which is not always obvious from the outside.