Hybrids are, for want of a simple definition, a combination of some material and acrylic.
Most of the time the material is a wood burl. Mallee and Maple tend to be a favorites amongst the makers of these really cool blanks, but so many burls can be used. The caps and unique shapes of the burl allow for incredibly cool patterns in the finished product.
Other times the casters use straight grain wood, or wood pieces to give it a jigsaw effect.
Pinecone, antler, banksia pods, and so many other thigns can be used in these really cool hybrids.
Here are some examples: