the quality of having great facility and competence
"Her proficiency in playing the violin allowed her to master complex pieces within months."
skillfulness in the command of fundamentals deriving from practice and familiarity
"practice greatly improves proficiency"
Ability, skill, competence.
"Her proficiency in French allowed her to negotiate confidently with local suppliers."
In plain English: Proficiency means having enough skill to do something well without needing much help.
"Her proficiency in Spanish allowed her to make friends easily while traveling abroad."
The word proficiency comes from the Latin present participle prōficiēns, which means "making progress." It entered English through the earlier form proficient to describe someone who is skilled or advancing in a particular area.