Entity interpolation
The client draws other players' entities slightly in the past and interpolates between the two most recent server snapshots, so their movement looks smooth despite sparse network updates.
The server sends state a few times a second, not once per frame. If the client drew each snapshot as it arrived, other players would jump jerkily. Entity interpolation adds a small buffer — typically around 100 ms — and renders remote objects in the past, smoothly interpolated between the two most recently received snapshots. The technique was formalised in Valve's Source engine.
The cost is latency: what you see of other players always trails the present. For your own character the client instead uses client-side prediction, and the server accounts for the delay with lag compensation when deciding hits. Together they hide the network's unevenness without it feeling wrong.