Investiture

Investiture is the word for someone who, or something which, has gained a portion of the magic of Adonalsium. It is a cosmere term, describing one of the core principles common to magic systems across the cosmere, whereby through some mechanism, people or objects can become Invested with various magical powers.

On Roshar, the Investing of an object is done by infusing it with Stormlight. Shardblades and Shardplate are Invested objects. That which is specific to Roshar is that Investiture manifest in the Physical Realm.

This has to do with the nature of the magic systems in the cosmere. They interfere with one another (i.e., Investiture resists Investiture). Something that contains a lot of power resists the efforts of magic to influence it. A strong spirit can interfere as well. The more Investiture something has the more difficult it is to affect.

This is the reason why Shardblades don't just slice through each other and why people wearing Shardplate are difficult to affect with Lashings.

Investiture left alone, especially in bigger amounts, will either look for some holder, or develop sentience on its own. The developing sentience might not be an easy or fast process, yet matter in the outer cosmere developed sentience too. Gaining sentience or sapience by Investiture is a cosmere-wide thing, and it started happening on its own on Sel, for example.