Tunisian crochet seems to be a hybrid of knitting and crochet, although you do not need to do either to be able to learn Tunisian crochet. It is worked on a long hook (this can be double ended or have a stopper on one end).
Stitches are picked up along a row, called a forwards pass and then worked back off the hook in a reverse pass.
The history of Tunisian crochet seems shrouded in mystery and there is a question as to whether it was actually done in Tunisia. There is evidence that it appeared around the same time as regular crochet in the mid-19th century by instructions being found in Europe and then not long after American publications picked up and published them. Later on, it fell out of fashion but was popular again in the 1960’s and 70’s where the basic simple stitch became known as Afghan crochet, probably as it was recommended for blankets, or Afghans.