The object is cut into a board of wood and may have undercut but usually doesn't have fully carved sides or backside.
For a good starting point, check Mary May's School of Wood Carving or her tutorial on how to 🎬 carve a simple flower
Cuts with various knive straight into a board, often decorative, geometric figures but also other objects.
Check this introduction to chip carving
Three dimensional carvings of objects from a block of wood.
For a facetted style, check these videos:
For whittling, check this channel:
Often done in green wood using axe, adze, hook knife and gouge.
See https://davidffisher.com/2017/04/08/getting-started/ for a low-threshold entry point in terms of tools.