A vocabulary bank is a collection of new words and phrases that the learner or class builds up as they learn.

Example
Some learners carry a collection of small cards with them. Each card has a word on it, with a definition or translation, and an example.

In the classroom
Vocabulary banks can be kept by individual learners, incorporated into language portfolios, kept as a class resource in the form of wall charts, recorded in a permanent area on the whiteboard during a series of classes, or stored on a class blog.