This relay has the following max contact voltage, current and power ratings:
Now focusing on the DC switching from the datasheet, the max switching current is 10A and max switching voltage is 30V. But the max power would be 10A×30V = 300W but it is given as 240W.
So does that mean how we interpret this datasheet would be different such as:
For max voltage 30V the max current should not exceed 8A.
For max current 10A the max voltage should not exceed 24V.
Is that what it means?
I believe your interpretation of the datasheet is correct. The DC safe operating area is bounded above by the maximum current of 10 A, to the right by the maximum voltage of 30 V, and to the upper right by the maximum power of 240 W:
All relay ratings are a compromise between capability, and lifetime. The manufacturer is making assumptions about how much life you'll be happy with, and is making guesses about whether you're switching resistive, capacitive or inductive loads. Hint, the first is kinder to contacts than the latter two.
These ratings should be regarded as guidelines. The relay will not have its full mechnical life if operated at 90% of these, it will not fail instantly if operated at 110%. You'll notice that the rated lifetime is 107 cycles mechanically, but only 105 electrically. That's the manufacturer telling you about the damage that is done to the contacts making and breaking a live circuit. You can expect the lifetime to be affected if you're gentle with it, or if you thrash it.
The mere fact that there is a power rating, as well as voltage and current ratings, should alert you to the fact that both the voltage and current can damage the contacts, and a large combination of them will damage them faster.
A 240 W limit means don't exceed 8 A at 30 V, don't exceed 24 V at 10 A, and don't exceed 26.6 V at 9 A.
