What's the big difference between Hidden and Spoiler?

Would people still have the option to read what's 'Hidden' like they would with 'Spoiler'?

Hidden means that only people who have posted in the particular thread will see the hidden content. Sometimes hidden contents are visible for all registered members even if they have not posted in the thread but in either case, they will not show to unregistered members.

Spoiler will hide the content but show it if clicked. Spoilers are good to use not only when you post actual spoilers but also when your post includes heavy media content like multiple videos or large photos/pictures.

I hope this helps .

Yes, this helps greatly since when I googled for an explanation nothing clear came up. Thank you!