The grammar translation method is a method of language instruction that focused on instruction in vocabulary and grammar, followed by translation activities from the L1 to L2 and from L2 to L1.
The medium of instruction was the students' L1. The assumption was that students would naturally pick up the ability to use the language if they obtained a full and explicit understanding of language rules.
It is not a particularly good method as there is no evidence that students actually learn languages through memorising grammar rules.
It was followed by the Direct Method.