What is the combination of salt water and fresh called?

There isn't a specific, universally accepted term for the combination of salt water and fresh water. However, depending on the context, you could use terms like:

General terms:

* Brackish water: This is the most common term for water that is a mixture of fresh and salt water. It's typically found in estuaries, where rivers meet the sea, and in coastal areas where groundwater mixes with seawater.

* Saline water: This term generally refers to water with a high salt content, but it can also be used to describe water that is a mixture of fresh and salt water.

More specific terms:

* Estuarine water: This refers to water found in estuaries, which are the transitional areas between rivers and the sea.

* Coastal water: This refers to water found in the area near the coast, which is often influenced by the mixing of fresh and salt water.

The most appropriate term will depend on the specific situation and the intended meaning.