Song style is a printed font, while regular script is a handwritten font.
Song style is a Chinese character font that appeared to adapt to printing technology. The strokes vary in thickness, and are generally thin horizontally and thick vertically. There are decorative parts (i.e. "foots" or "serifs") at the ends. Strokes such as dots, strokes, strokes, and hooks have tips, and they belong to serif fonts. Commonly used for text layout in books, magazines, and newspapers.
Regular script is also called Zhengkai, Zhenshu, and Zhengshu. It gradually evolved from the official script and became more simplified, horizontal and vertical. "Cihai" explains that it has "a square shape and straight strokes, which can be used as a model." This kind of Chinese character font is correct and is the modern traditional handwritten Chinese character.
Extended information:
The culture of the Song Dynasty flourished, and the printing industry developed greatly. From the Southern Song Dynasty, fonts similar to block letters began to appear in printing workshops in Lin'an and other places. Later generations called it imitation Song style. During the Ming Dynasty, literati sought to engrave books from the Song Dynasty, so engravers thickened the vertical lines and stroke endpoints imitating the Song style to resist wear and tear on the engraving, but they still called it "Song style". The modern so-called Song style is basically formed in this way.
Kaishu is also a kind of official name. "New Book of Tang·Hundred Officials 2" records that there were 20 regular script writers in Zhongshu Provincial History Museum and 18 regular script writers on national history. As an official name, regular script is also called regular script hand. The person in charge of writing is juxtaposed in the same organization, and the specific division of labor is different. "Tongdian·Twenty-Two Officials" records that the regular script writer is an official with outstanding honors from outside. In the Song Dynasty, there was no regular script calligrapher, only regular script.
Reference materials:
Song style-Baidu Encyclopedia
Regular script-Baidu Encyclopedia