8b/10b encoding is kind of like a secret language that computers use to communicate with each other.
Imagine you have a special set of 8 toys, and you want to send a message to your friend who also has the same set of toys. But, you also have 2 extra toys that your friend doesn't have, so you need to figure out a way to include those extra toys in your message.
So, you come up with a code where you assign each of your 8 toys a special set of 10 toys. When you want to send a message using these toys, you first convert each of your 8 toys into its special set of 10 toys, and then send those as the message.
When your friend gets the message, they can convert the special set of 10 toys back into the original 8 toys, and they'll understand what you're trying to say. And because you're both using the same set of toys and the same code, you'll always be able to understand each other's messages.
8b/10b encoding works kind of like this code. It's a way for computers to take 8 bits of information (which can represent any letter or number or symbol), and convert them into a special set of 10 bits. When the message is sent to another computer, it's converted back from 10 bits to 8 bits so the receiving computer can understand the message.
This helps to make sure that the message is transmitted correctly, because if there are any errors or bits get lost along the way, the receiving computer can tell that something is wrong and ask the sending computer to send the message again.