A wolfling run is basically letting your game run without intervening in your norn's lives. There are four variants of this, and one alternative.

A strict wolfling run is where you hatch a group of norns in the plain Albia or on the Ark, with no additional COBs or agents, and leave them to grow up by themselves for a period of time without interacting with the game at all.
A relaxed wolfling run is where you set up the world before you begin the run, adding any COBs, agents, metarooms or worlds you like, but once the run begins you are no longer allowed to interfere with the game for the remainder of the run.
Also, a "Forum Wolfling Run" can be run, where entrants are sought from the collections of the community, often named after their owners, and set loose in a world together, the gamemaster updating the owners of the entrants on a forum thread, often with pictures. The forum wolfling run can be either strict, or relaxed.
A Global Wolfling Run is exclusive to Docking Station - each player sets up their world according to some commonly-defined rules, and sets it to warp only between the members of the GWR. This is described as being more like an ecologist's fieldwork.
An alternative to a wolfling run is a feral run. This information was taken from here.