The one-way connection going in the direction FROM a network and/or server (such as a mobile phone network) TO an end-user device (such as a phone).
A two-way (bi-directional) connection generally contains both an uplink and downlink connection.
An asymmetrical two-way connection has a faster maximum speed (data rate) in one direction than the other. Typically, the downlink / download direction is the faster one.
See: Uplink