There are some A's, some O's and some T's under the font folder. What do they mean?

A stands for Font format extended font, which was handed down from the old 16 bit system. Generally, it is a dot matrix font, and different font sizes must make different fonts. For example, the default Fixedsys font of XP Notepad in the system belongs to this font. T stands for a font with ttf or ttc extension. Ttc(TrueType font) is a collection of various ttf fonts. Ttf font was developed by Microsoft. This font technology can see the actual printing effect on the screen without distortion. O(OpenType font) refers to the font file with otf extension or OpenType font file with ttf extension, which was jointly developed by Microsoft and Apple. It is more accurate than ttf font curve and is used for high quality printing. Ttf and otf are both mainstream font formats at present.