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 (WCAG Level AAA).

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 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