The question comes with no relation to a specific product, so it's hard to interpret what you want to know.
"Chicken bit" is a general term used in silicon chip design, for example for our MCUs and MPUs.
It is a bit which can be used to enable/disable functional blocks inside the chip. This can be IP blocks like Ethernet MAC or CAN, but also additional CPU blocks. We use this method to offer various chip configurations to the market based on the same silicon die. Normally these bits are OTP (one-time-programmable) and they are not accessible by the end user. We program these bits during production on the chip tester and then this area is locked against further access.