I hear this word all the time when watching tv. The English translation says it means truth/reality. I know languages aren't meant to match up meanings and I'm guessing this word has a different usage.

Could someone please help me better understand. Thank you.

That's what it means.

"I ate dog once."
"Really?" <- You could use hontou here. It would mean something more along the lines of "Honestly??" in a literal sense though.

"I really love this shirt." <- You could use hontou instead of really here as well, similar to the above sense.

"It's true that I'm 2 meters tall" <- Here you could use hontou for true.

So basically, it either means "true" or "honestly".

It means truth/reality
You could also say it gets used as "really?" (本当？) or "is that true" (それは本当ですか), though arguably true and really come from truth and reality

I truly love 本当に. Verily, I assure you.

本当 is often paired with the に particle.
Here are some common examples:
本当（に）？　 Really? (に is toally optional here)
僕は本当にうそを附きません。 I'm honestly not lying!
M：むりでしょう。　　　　　　It's probably impossible
F：本当ね。 True.

I hope that helps!

I thought wrong then, lol.

Thanks all.

*EDIT*
I didn't have time earlier. But yeah, I didn't know it could mean "really?" which is a very common word. I was taking it to literally.

Thanks guys, you've made it a lot easier on me when watching tv now.

o rlly?

本真っすか？