Cum
This is the latin word meaning "with".
Basically it describes any rights or privileges attached to owning a security. For example, a share bought or sold cum a benefit, confers that benefit on the purchaser.
Among the common phrases you may run across are: cum rights; cum dividend; cum scrip; cum capitalisation. So, if you acquire shares in this state, you'll get the added benefit noted!
Conversely if you buy shares ' ex ' dividend, you won't have the benefit of the dividend payout.