as a rule; frequently; usually
"People commonly forget to lock their doors when they leave for work."
In plain English: Commonly means something happens most of the time or is true for many people.
"People commonly use public transport to get around the city."
Usage: Use commonly to indicate that something happens frequently or is standard practice in most situations. Place it before the main verb or after the subject to clarify that an action occurs as a general rule rather than always.
Commonly comes from Middle English comunly, which was formed by adding the suffix -ly to the word common. The term has retained its original meaning of "shared or widespread" as it traveled into modern English usage.