This year STEM Expo has drastically revised the categories to be more inclusive, and separate out multiple scientific fields into more specific sectional groupings.
We're keeping all the fun stuff, but adding a methodology to broaden our horizons as we continue to expand.
Although the specific details will not be available until the full category descriptions and rubrics are released (on or before December 1, 2017), you can see what the base category descriptions are by following the link to the Category Descriptions.
The largest category in previous years has been the "Scientific Inquiry" category. This category is no longer available, but instead we've revised all the others to split that one out. We've created a document (here and below) that has some entries from a previous year's event split to the new categories as examples.