Final answer:
The difference operation in relational algebra is denoted by the Greek letter delta (Δ), representing the tuples present in one relation but not in another.
Step-by-step explanation:
The relational algebra operation denoted by the Greek letter delta (Δ) is called the difference operation. It is used to find the tuples that are in one relation but not in another. The difference operation subtracts the tuples from one relation that match with the tuples of another relation.