If something is secreted, it is produced and released by a living thing, often in a way that is not easy to see or find.
The word secreted is often used in science and medicine to talk about how living things make and release things.
Examples:
The plant secreted a sweet smell.
The animal secreted a sticky substance.
She secreted the treasure in a hidden place.
The tree secreted a special juice.
The spy secreted the important papers in his shoe.
The flower secreted a magical potion.