английский => русский Техника Компьютеры (в целом)

In Statistical Machine Translation, customized machine translation engines are created based on a large amount of project-specific training data, usually a TM of at least one million words. A statistical mechanism creates a translation system on the basis of this input, ***using a baseline of a minimum of 300 millions words as back-off to cover the basic words and patterns in any language.*** The MT output is therefore very specific to this project, mirroring the existing material as much as possible. This means that the machine translation for each project will behave differently as the training material will be different. It also means that the quality of the machine translation will correspond to the quality of the training material.

Не очень понятен выделенный отрывок. Вначале там говорят про 1 миллион слов, и тут же их сразу в 300 раз больше. Откуда? Возможно, ответ кроется в слове back-off, но мультитран и поиск по прозу мне не раскрыли его смысла.

Спасибо