A text message containing information (usually unflattering or damaging) about a third party which is sent to the individual it concerns rather than the person for whom the communication is intended.
Text written for secret lover is inadvertently sent to partner, making it a mistext:
"On my way home, partner name suspicious, don't call."
A misunderstood text due to many factors but mainly due to the fact that you don't know the other person well. Most notably when you start dating and should be talking and not texting!
I was texting my new girlfriend and we got in a stupid fight due to mistextulation. That shit is so annoying and so easily avoidable.