Stream order is such that the top headwaters of a stream are stream order 1, when two of these meet, this becomes a stream order 2 stream, etc.
Processing notes: StreamOrderEdit attribute is the NHDFlowlines Snapshot joined with the NHDPlus Value Added Attributes table, and then a new field created, which is Stream Order, except that all Null stream order values were changed to 1. This data layer is also just the StreamsRivers of the NHD in the clip area. In the future, these small streams maybe should be an attribute of 0.5, indicating that they are intermittent (which looks to be the case in many of the Null streams).
To see where the Null Valeus were, see the layer with Null Values mapped: https://databasin.org/datasets/fd4846dea98341338eb94b1bc35e04ff