The quality of state of being proficient; advance in the acquisition of any art, science, or knowledge; progression in knowledge; improvement; adeptness; as, to acquire proficiency in music.
Mastery or ability to do something at grade level. California students receive scores on the California Standards Tests (CST) that range from "far below basic" to "advanced." The state goal is for all students to score at "proficient" or "advanced." (Ed Source)
Proficiency consists of the learner's knowledge of the target language; it can be considered synonymous with 'competence'. 'Proficiency' can be viewed as linguistic competence or communicative competence. L2 proficiency is usually measured in relation to a native speaker's proficiency.
the quality of having great facility and competence
the learning stage concerned with accuracy and fluency.
ability to communicate effectively in both oral and written forms in the cultures where the language is spoken. Proficiency is made up of three components: function, content, and accuracy.
how well a person functions in a language