Type propagation is an analysis step in the LabVIEW compilation process that resolves data types for terminals that adapt to different data types and detects syntax errors. This step runs each time you edit a VI.
For example, if you wire an integer to the input of the Decrement function, the data type of the output is an integer. If you wire a floating-point number to the input, the output is a floating-point number. The same pattern exists for arrays and clusters. This behavior of determining the output data type based on the input data type through the block diagram is called type propagation. If you wire an enum to the input of the Decrement function, the type fails to propagate through the block diagram and the VI reports a syntax error because decrementing an enum is not a legal operation for this function.