A stroke is a single movement of the writing instrument, in modern times most commonly a pen, pencil, or writing brush.
The Eight Principles of Yong (永字八法) explain how to write eight common strokes in regular script which are found all in the one character, 永. It was traditionally believed that the frequent practice of these principles as a beginning calligrapher could ensure beauty in one's writing.
In the twentieth century, drastic simplification of Chinese characters took place in mainland China. However, the basic rules of stroke order remained the same. Taiwan continues to use the unsimplified forms, often called traditional or regular forms.
