What does fully modded mean in terms of Dota 2 Items?

Can someone explain me what it means if an Item is fully modified in Dota 2 ?
Like Odachi full mod for example.

Full mod means that the item (in that case the Fireborn Odachi for Juggernaut) has been socketed with the maximum amount of gems possible.

With your example :

The Kinetic gem that gives a custom animation to blade fury and the 3 Inscribed gems that respectively track the number of Omnislash jumps, the amount of blade fury damage and the number of blade dance crits.

It's related to dota 2 items. You can modify your items. Odachi Fireborn, correct me if I am wrong, is a Yunero Juggernaut Dota 2 Sword.

Full mod means fully modified aka maximum modified (max gems socketed)

Here you can see more about it :

dota 2 trade screenshots odachi mod