The Johannine comma is a fancy term for a disputed Bible verse that talks about the Holy Trinity, or the Father, the Son, and the Holy Spirit. The verse is found in 1 John 5:7-8 and was added in some versions of the Bible, but not others.
Here's the thing: some people think that the verse was added later on, after the Bible was originally written. They believe that it wasn't there in the very beginning, which means it might not be true or accurate.
Other people, however, think that the verse was always a part of the Bible and that it's an important piece of scripture. They believe that it should be included in all versions of the Bible.
So, to sum it up: the Johannine comma is a debated Bible verse that some people think is important and others think is not necessary or accurate.