A glossary is a lexica that contains terminology to be used or not be used in the translations. It's here to aid human translators to use the terms preferred by your organisation.
You can enable the glossary by uploading a file... (currently, both tbx and utx glossary files are supported)
or by manually adding and defining the terms:
In the focus view, on every segment on the right side you will see the terminology based on the source text (suggestions for term usage) and your translation (approved term usage, suggestions for alternatives):