der Kai
quay
A reinforced waterfront wall in a harbor or along a river where ships can dock to be loaded and unloaded.
Das große Kreuzfahrtschiff machte am Kai fest.
The large cruise ship docked at the quay.

quay
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quay
A reinforced waterfront wall in a harbor or along a river where ships can dock to be loaded and unloaded.
Das große Kreuzfahrtschiff machte am Kai fest.
The large cruise ship docked at the quay.

A related word is 'die Kaimauer' (quay wall). It describes the wall of the quay and helps you imagine the meaning as a solid, wall-like bank reinforcement in a harbor.
Die alte Kaimauer wird derzeit saniert.
The old quay wall is currently being renovated.
Pay attention to the preposition and the case: 'am Kai' (at the quay) with the dative describes a fixed location. 'An den Kai' (to the quay) with the accusative describes movement toward it.
Das Schiff liegt sicher am Kai.
The ship is safely at the quay.
In connection with 'Kai' (quay), verbs related to shipping are often used. Typical combinations are 'am Kai anlegen' (to dock at the quay), 'am Kai festmachen' (to moor at the quay), or 'am Kai liegen' (to be docked at the quay).
Ein großes Containerschiff hat am Kai angelegt.
A large container ship docked at the quay.
bank / shore
'das Ufer' and 'der Kai' both have to do with the edge of a body of water. 'Ufer' is the general word for the strip of land directly by the water, for example along a river or lake. 'Kai' is used for a reinforced place, usually in a harbor, where ships can dock. Learners may confuse the words because a 'Kai' is also located on the shore or bank. In practical terms: you can go for a walk along the 'Ufer'; ships are often docked or stopped at the 'Kai'.

Heute legt das Schiff am Kai neben dem alten Lagerhaus an.
Today the ship docks at the quay next to the old warehouse.
Am Abend läuft der Fahrer noch eine Runde am Ufer entlang.
In the evening, the driver takes another walk along the riverbank.