Arial is a sans serif typeface, designed in 1982, based on Monotype Grotesque. The font has a similar proportion and weight to Helvetica.
It is a font with a contemporary look. Since 1992 it has shipped with every version of Microsoft Windows, which has helped it become ubiquitous.
It is a favourite of desktop publishers, though less so with designers; who think it inferior to Helvetica. The story goes, that it was designed primarily to avoid having to pay royalties (to Linotype) for the use of Helvetica.
It is rarely recommended for print work (though it is a print font). Helvetica is considered a better-looking, more flexible font.
Arial and accessibility
Arial is recommended by RNIB and other organisations concerned with accessibility. If you search for guidelines for document accessibility they all tend to say, use Arial, with a minimum size of of 14pt.
However, I am not aware of any research that shows Arial to a better font than similar sans serif fonts. I think it’s more likely that it was the sheer ubiquity of this sans-serif font that led to the recommendation.
There are similar contemporary-looking, clean and easy-to-read fonts that would do the job just as well. I.e. Calibri, Century Gothic, Helvetica, Tahoma, and Verdana or Myriad Pro.
Note that all of the above fonts are sans serif. Serif fonts are rarely recommended – as more ornate fonts are considered more difficult to read. On lower resolution computer screens the serifs can be distorted, making the words look blurry.
Slab serif Fonts
Having said that, slab serif Fonts (a type of serif typeface characterized by thick, block-like serifs) such as Rockwell, Clarendon, and Museo Slab are considered easy to read and accessible. They tend to be used for headings rather than body text.
Photo: “Pool of Knowledge” by Ian Muttoo is licensed under CC BY-SA 2.0