A false memory is a memory that you think is real, but actually there is nothing real about the memory. These can be created by someone else telling you a story that may or may not have actually happened to you in the past but that you do not actually remember. After hearing this story, your brain creates a “memory” of the event. This isn’t actually a memory that you had, someone else put it their.
This reminds me of my sister. Constantly when we were little, she would tell me crazy stories of things that happened to us that I knew had never happened. Since she did this all the time and I knew these things hadn’t actually happened, I didn’t create a false memory of them, but my sister may have created a false memory of these things happening.