A spot trade in general refers to a trade with immediate delivery. In energy trading terms it usually refers to a trade with delivery on the day it is executed (within day) or for the following day (day ahead)

Detail

There is usually high volume trading in spots, particularly for power and gas, as speculative traders try and close out their positions as delivery times approach, and asset-backed traders try to balance, and financially optimize their positions. A large proportion of spots are traded on Exchanges and through Brokers

Spot trades are settled physically, and even if executed on an Exchange are often settled by invoice and payment within a day or two of delivery