refers to the regular weight of the font (as opposed to Bold or Italic).
Arial is proprietary software owned by Monotype Imaging. While the basic version is bundled free with Windows and macOS, you are not legally permitted to redistribute the raw font file. If you download "Arial Normal" from a third-party site, you may be violating copyright. Arial Normal Panose Default Font Download Extra Quality
For Arial to function correctly as a system default, you need a clean, properly licensed, and fully hinted version. refers to the regular weight of the font