Source: Warhammer Fantasy: 4th Edition

Snaking
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A unit deployed in a long line with models lined up one behind the other can manoeuvre very easily. The lead model is not restricted by troops either side and so can choose a snaking path which twists about. This is called snaking. Trailing models are placed so that they follow the path of the lead model. This a special type of movement unique to long lines of troops. It isn't a very practical formation for fighting, but it is very handy for threading your way through buildings and other obstacles.

snaking
A unit deployed in single file can 'snake' forming a long twisting line.