In the photograph, conventional forward current through the diode flows from positive on the left to negative on the right. The wire on the left is the anode and the wire on the right is the cathode, often denoted by "a" and "k". A black band on the actual object denotes the cathode. In the schematic symbol the flow of conventional current is shown by the direction of the triangle, so the top end is the positive anode and the bottom end is the more negative cathode. When it's working in the circuit, you could measure across those two points with a multimeter and see something like +0.65V, which is the forward voltage (Vf) of a standard silicon signal diode.
You could get confused, because in the circuit, positive conventional current is actually flowing out of the cathode with respect to the 0V rail. This is the opposite to what you would see with a battery. This is why some electronics engineers have been known to refer to a diode cathode as, "the pointy end," when crafting change requests to schematics involving the production of millions of mobile telephones. In such circumstances, where the person editing the controlled schematic diagram may not be an electronics engineer, you can never provide too much information.
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03-MAY-2026: canonicalised, direct refs