What is Data Fusion?

Legal Definition
Data fusion is the process of integration of multiple data and knowledge representing the same real-world object into a consistent, accurate, and useful representation. The goal of data fusion is to combine relevant information from two or more data sources into a single one that provides a more accurate description than any of the individual data sources.

Data fusion processes are often categorized as low, intermediate or high, depending on the processing stage at which fusion takes place. Low level data fusion combines several sources of raw data to produce new raw data. The expectation is that fused data is more informative and synthetic than the original inputs.

For example, sensor fusion is also known as (multi-sensor) data fusion and is a subset of information fusion.
-- Wikipedia
Legal Definition
Making raw data from sources to get better information. It is more useful than a single source of data.