Acronyms and abbreviations should be spelled out the first time they are used on a page with the abbreviation in parentheses. 

A mechanism for identifying the expanded form or meaning of abbreviations is available to be in compliance with the Level AAA Web Content Accessibility Guidelines (WCAG).

Do not use symbols and abbreviations (including symbols like ‘ for “foot” or x for “by” or a dash for “through”) as that will not translate. Exceptions include using the percent symbol instead of writing out “percent” within the content and using the slash symbol to represent fractions (1/3).

• Example: The World Health Organization (WHO) has indoor air quality guidelines.

Resources 

• Editor Widget Overview
• Label Abbreviations in the Editor Widget
• WCAG Guideline 3.1.4 - Abbreviations