A Toy Language is a language that was invented to serve no useful purpose (though it might by accident) other than to fulfill the whim of the creator. They are sometimes known as esoteric, tarpit, or "hey look at this language I created" language.
In researching the topic I learned that they actually have a more commonly used name: Esoteric Languages. Personally I prefer the term toy language over esoteric language, as nothing I can easily find with a google search is really all that esoteric.
In fact you can find all these esoteric languages through google:
Either way they are fun to read about and play around with.