TM stands for TranslationManager/2. TM/2 originates from the IBM TranslationManager tool and has been made available to the open source community.
TranslationManager/2 is a computer-assisted translation system (CAT) that automates repetitive tasks, freeing the professional translator to attend to the finer points of translation that require the judgement of an expert. TranslationManager/2 helps accelerate turnaround time and save money in overall translation costs.
It does not only help you tackle the vast amount of translation needs efficiently, but also frees you from tedious routine work inherent to translation projects.