Comparing Performance and Proficiency

In describing language ability, the terms performance and proficiency both refer to evidence of what a language user is able to do with language. Similar strategies can be used when teaching for both performance and proficiency. Likeweise, assessments of both performance and proficiency reflect purposeful communication tasks, mirroring real-world uses of language. There are also significant differences between performance and proficiency. What does each indicate?

(Direct quote from ACTFL Performance Descriptors for Language Learners, 2015).