What is Potato'd / Potato?

[Mewm]

I've seen the word a lot in Warframe and have no idea what does it mean, anyone can expalin?

[Suzaku]

A "potato" is an Orokin Reactor or an Orokin Catalyst. These items double the mod capacity of a warframe (reactor) or a weapon (catalyst). More mod capacity = more power, so these items can add more power and flexibility to your frames and weapons. Any frame/weapon that has had a reactor/catalyst installed is referred to as "potatoed".

It is safe to add a reactor/catalyst at any level, as it scales with the weapon's level. Using forma will not remove a reactor/catalyst. Selling a weapon, or using it as material when crafting a dual-wield version will not save the reactor/catalyst, so only use them on things that you plan to keep.