Theory of Mind is the ability to understand that other people have different thoughts, beliefs and feelings to those of your own. It is the capacity to imagine what another person might be thinking or feeling in any given situation, and the ability to take a guess at their intentions. It is also known as empathy.
In my observations, for an autistic person, it must seem like the world is filled with a bunch of neurotypicals who have no empathy. Autistics are constantly judged by neurotypicals, punished, assessed for their deficits and weaknesses, stared at, and moulded into different people to who they want to be within themselves. They are told they need to be cured, that the way their minds work is a disease, and is quite simply not acceptable.
To add insult to injury, autistic people are constantly told by neurotypicals that they have no empathy or Theory of Mind.
Can you see the irony here?
Check out this article for a deeper understanding of Theory of Mind and why it matters how we discuss it:
Psychology Today: Guide to Reporting on Autism: Theory of Mind & Empathy