The following is an excerpt from page 8 of the Warhammer Annual 2002 release with an expanded explanation by Gav Thorpe regarding the Skirmishers as lone models.

There is quite a long section in the Warhammer rules detailing how single characters on foot can move independently. This was to give characters on foot greater flexibility, to offset the advantages of characters mounted on steeds or monsters.

A simple way to think of characters on foot is as lone skirmishers. This means that they get all of the normal benefits and limitations of a skirmishing unit. This includes things like being able to shoot or charge in any direction, and also having no flanks or rear unless they are already engaged in combat. When played properly, a character on foot can prove more useful than one on a big ravening Dragon or Wyvern.

However, you should also remember that characters outside of units can be horribly vulnerable to war machine fire (and other missile fire if too far from friends) as they no longer have their "Look Out, Sir!" special rule. Like all skirmishers, lone characters on foot have to fight in conjunction with other units to achieve their potential.

These rules only apply to vaguely man-sized characters on foot. Large characters follow all of the normal rules for units, marching and so forth (see page 135).