My English teacher explained about themself and themselves.
I don't really quite understand though.
closed as unclear what you're asking by tchrist, Hellion, Jon Hanna, choster, phenry Jul 8 '14 at 16:59
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Themself is himself or herself when you don't know the gender or simply wish not to disclose it. There's even something more intricate here. There's "they" that is singular too!
Don't be fooled by the them part. It's still a singular. I find that confusing too.
In the future, provided that your English is at a beginner level, you might want to get more patient and rewarding answers if you turn to the other English-related site, the one for learners.
Here, you might ask a question like: "in what century did the word themself start to be spelled in the modern way and why did that happen".