For multi-level marketing: all those participants whose sales result in a commission for X. These lie in the descent group of X (descent defined by recruitment). For money chain letters: all those letters with X's name and address on the senders list.
In a network or multi-level marketing company, your downline are the recruits that you find to also join the company. In multi-level arrangements, your downline will also include the recruits of your recruits.
Refers to affiliates who are below you in the T-Net network.