'Secret' in the Bible

Then Pharaoh also summoned wise men and sorcerers, and the magicians of Egypt by their secret arts did the same thing.

But the magicians of Egypt did the same by their secret arts, and so Pharaoh's heart remained hard, and he refused to listen to Moses and Aaron -- just as the Lord had predicted.

The magicians did the same with their secret arts and brought up frogs on the land of Egypt too.

When the magicians attempted to bring forth gnats by their secret arts, they could not. So there were gnats on people and on animals.