It is an irregular form of the imperative mood of verb "vidět"/"to see". See https://en.wiktionary.org/wiki/vid%C4%9Bt
It is now used mostly as a fixed expression.
If you meet "viz." it is something similar, but international https://en.wikipedia.org/wiki/Viz.
The similarity of these (Czech "viz" and Latin "viz.") is a common source of confusion.
"Věz" and "jez"? Yes, verbs " být, jíst, vědět, vidět, mít, chtít, jít" are irregular. You cannot place them into those 5 classes of regular verbs.
The list of Czech irregular verbs differs from article to article. The English Wikipedia has many https://en.wikipedia.org/wiki/Czech_conjugation#Irregular_verbs But some of the irregularities are only in one or two forms and the verbs do belong to one of the classes. The Czech Wikipedia lists fewer of them https://cs.wikipedia.org/wiki/%C4%8Cesk%C3%A1_slovesa#Nepravideln%C3%A1_slovesa