Japlish is when Japanese people use words or phrases from English, but they don't always use them correctly. It's sort of like when you try to speak a language you're not very good at and sometimes make mistakes.
For example, imagine you're playing with building blocks and you say "Me wants more blocks." Instead of saying "I want," which is the correct way to say it in English, you added "me," which is wrong. Japanese people might do something similar when they mix up English words and grammar.
Japlish is pretty common in Japan because lots of people learn English in school, but they might not have many chances to use it in real life. So when they do use it, they might make mistakes. But that's okay, because everyone makes mistakes when they're learning something new!