There are multiple definitions - click on the translation that matches your context.

a saber

advérbio

full

viz.

adverb

Definitions of viz.

namely; as follows; that is to say; that is; in other words (used to introduce an explanation of what has just been written)

The court overruled the objection on the ground that Benson's statement was not introduced to establish the truth of its contents (viz., that the gun belonged to Furr).