It's a "100% stacked bar chart", see examples here. Only that in your case you have only one bar instead of many.
Here's a bit more on its characteristics that determine how the name is composed:
- 100% because it includes all possible components and they add up to 100%
- stacked, because they all show up on top of each other (as a single line) rather than side by side as conventional bar charts
- it is also horizontal (left implicit above)
- there's also an implicit reference line pointing at the middle
- and clearly it falls into the wider category of bar charts