On: IronCalc – Open-Source Spreadsheet Engine

[bonoboTP]

Backend is a general word, not limited to client-server or the web. You can have a rendering backend with various configurable choices, like in Matplotlib (https://matplotlib.org/stable/users/explain/figure/backends....), or the deep learning library Keras has a choice between PyTorch, JAX and TensorFlow backends.

[fsckboy → bonoboTP]

we're talking about a spreadsheet engine, the backend is not going to be the Xserver displaying it