Mui Fah or Plum flower stumps, are small posts inserted into the ground, for the student to practise his horse work and footwork patterns on. They can be placed even into the ground, or they can be set up so the posts gradualy rise, so not only is the student working on balance but has the added work of slowly walking "Up Hill".
The Standard pattern is a 5 point Plum flower, that is used in training the Yee Mah? Methods. This training is a very very old idea found in most Kung Fu Systems. It is unknown to the extent that the Wing Chun Ancestors specificaly used this method of training.