Assign

What Does Assign Mean?
The act of clearing houses and brokerages selecting short option and future contract holders to deliver underlying securities or commodities of maturing or exercised/tendered contracts.

Investopedia explains Assign
Not all contracts will typically be exercised or tendered; those that are need to be settled with delivery of the underlying security/commodity. Most often, clearing houses will randomly allocate assigned contracts to brokerages that, in turn, randomly select which of their clients will be assigned.