What is the meaning of the character 打 in 打坐?
According to the 《佛光大辭典》,

打坐
指跏趺而坐 (to sit cross-legged)，使心入定 (to settle the mind)。
即指坐禪 (za-zen, to meditate)。
「打」，動作行為之意 (means to do or to act)。

According to the 《汉语大词典》,

打 (36)
谓从事某种工作 (to do some kind of work) 或做出某种行为 (to make some kind of behavior)。

Therefore, the 打 in 打坐 means &quot;to do&quot;, and 打坐 is &quot;to do the 靜坐&quot; (to sit still with a peaceful mind).
Since the purpose of 打坐 is to settle the mind, it refers to meditation.
(dan chose 打(38) in the 《汉语大词典》.)