What is Ladder?

I was looking up Runewords and one, Mosaic, stated that it was Ladder only.
What is Ladder and how do I see if I can use Mosaic?

There are only a few runewords that are ladder only, and that's currently the only difference between L and NL.

here is the list :
Mosaic
Hustle
Cure
Metamorphosis
Bulwark
Hearth
Ground
Temper

New ladder just started yesterday, so if you want one of them, time to start it, as at the end of ladder the ones made will transfer with your char to NL.

when u create a new toon, u have the option to make it a ladder character. ladder characters do not share stash and can not trade with non-ladder characters. each ladder season lasts ~ 4 months, after which they become non-ladder.

season 7 starts tonight

Just to add some corrections to the above, season 7 didn't start yesterday. It also doesn't start tonight. It starts 2024-05-24T00:00:00   This timestamp has been automatically converted to your local date/time for convenience. The format is DD/MMM/YYYY, HH:MM am/pm. This is based off your browser time. .
See "patch" notes:
As for the OP, ladder is simply a different game mode. It is largely the same as non-ladder with the

Key difference being that ladder is functionally separate, meaning you won't have access to any non-ladder gear or characters within ladder, and ladder is divided into seasons (see above for season 7 start time). At the end of each such season, all ladder characters and gear/stash from said season are converted into non-ladder before the next season starts.

As a result, you're basically looking at "the same thing" except that every so often, everyone will be put back on even footing with everyone else as everything is reset for the new season.

Other than that, the only real difference is that ladder allows you to create the handful of ladder-only runewords available. Realistically however, that isn't too big a deal as those haven't changed for a few seasons now and as each season ends, the ones that were created on ladder are converted into non-ladder items. So while you can't create the ladder-only RWs from scratch on a non-ladder character, you can trade for them and use them on non-ladder as plenty of them have been converted down.

Back in the olden days, the item difference was a lot more significant (more top-end RWs, uniques, cube recipes, ...).
Also, back in the olden days, ladder was actually more difficult as well (as it buffed mobs a tad) which may or may not be true anymore with D2:R (never bothered to confirm) though that difference wasn't really anything to write home about either and largely unnoticeable.

If you don't want to create ladder characters (my case...), the only way to obtain those runewords is trading...

A quick addendum: If you are playing on offline all runewords will be available to you even the Ladder exclusive ones (they made it like that so you are not hardlocked out of game content).

P.S. Ladder is basically a competitive game mod that represents a race to lvl 99 in a 3 months period (usually) for the leaderboards and everything people stated above.

Brand new economy is the big thing

Fun Fact: Spirit used to be *ladder* only.