Language laboratories over time have often been referred to as having a "level," meant to be a descriptor regarding the broad teaching/learning capabilities of a lab's primary equipment systems. These level designations were prominently used by equipment vendors in the 1980s and 1990s, suggesting a possible manufacturer-centric origin for the terms. In any event, the descriptors were adopted by language laboratory facilities and became part of the professional vernacular.
The aptly given nickname "dial-a-language" denotes old lab systems (late 1960s into the late 1970s) which used analog channel switches to route audio signals to (and occasionally, from) student stations to master recorder decks. Such schema typically included the playing of audio material (sometimes on arbitrary schedules) to which students could listen by selecting the corresponding channel.
These systems were most appropriate in group settings, when a class might collectively listen to an audio track (of a workbook lesson, for instance) and follow along together. Despite its leanings in this direction, there were attempts to play various lessons during a variety of times, for individual student study outside of class. The plan included students checking into the facility and joining the recording (often well in progress), in hopes of following along in some productive manner. In this vein of use, these systems had obvious issues and a number of limitations, and though they were somewhat difficult for students to utilize independently, they were nonetheless an ardent stride forward in the pursuit of providing technology to students.