Storage temperature means the temperature that the device should be kept at while it is in the shelf.....while it is in storage...not being used
Operating temperature refers to the temperature at which it should be kept while it is in a circuit. You should make sure to keep the temperature of the device from exceeding this value while it is operational (current is flowing through it)....if too much power is being dissipated (while remaining under the power rating) but cooling is not available, the temperature of the device may exceed this value. and the device may get permanently damaged.
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