Blissymbols are a special type of writing system that use pictures or symbols to communicate. You can think of them like a secret code that only certain people can understand.
The person who created Blissymbols, Charles Bliss, wanted to make a way for people from different countries to understand each other without knowing each other's languages. So he came up with a bunch of pictures that represented different words and ideas.
For example, instead of writing the word "dog" in English, you could use a picture of a little doggy. And instead of writing the word "happy," you could use a picture of a smiling face.
Blissymbols are really useful for people who have trouble speaking or writing in regular languages because they can use the pictures instead. They can also be a helpful way for people who speak different languages to communicate with each other.