Why are my threads "locked"?

[PokeManiacNick]

I know that I haven't been doing much activity lately, but how come the majority of my threads are locked? I can't write replies, edit, or delete them in any way.
Is there any explanation why is it locked and what could I do in the future to prevent this?

[Agro]

Threads that haven't had a post in over 21 days in the most popular sections are auto-locked for inactivity. Feel free to recreate these threads or, if you really want to use the originals, PM a mod to unlock it.

[PokeManiacNick]

(Feb 1, 2017, 04:18 PM)Agro Wrote: Threads that haven't had a post in over 21 days in the most popular sections are auto-locked for inactivity. Feel free to recreate these threads or, if you really want to use the originals, PM a mod to unlock it.

Ah, that makes much more sense!
I'm a newbie to this site and this explanation means alot to me, thank you!