In Ontario, Canada during municipal elections many citizens living in rural areas will see election signs encouraging them to vote for "reeve". Being a city dweller, I recently saw such a sign on the way to the cottage for Thanksgiving and was perplexed. After asking around, here’s the definition I got from the rural folk:

The Reeve is just like a mayor, but instead of looking after a town or city, the Reeve is responsible for a "county", "township" or "area". Since the population of central and northern Ontario is so scattered, there are no major population centres that warrant a mayor. Therefore, a "Reeve" is elected to oversee the entire area.

"Reeve" is derived from the word "shirereeve". In times past, the Shirereeve was responsible for not only local government affairs but also law enforcement. As time went by, the position of "Sheriff" was established with the primary goal of law enforcement, leaving the "reeve" side of the word to handle the political end of things.

Basically, a Reeve is a Mayor, when there’s nothing to be Mayor of. For example, its possible for one to be the Mayor of the Town Exampleville, since the town limits and borders are established. However, when the area in question is bounded by "that river" to the north, "that road" to the south and forests to the east and west, and contains a number of one-horse towns, people are more comfortable with "reeve" for some reason.