CUDA is Nvidia’s conputation toolkit and language. it opens up to developers ways to accelerate tasks using the GPU. GPUs are usually really good at doing 2 things better than CPUs, Floating point math, and linear algebra (think a gpu to be like thousands of dumb smaller cores vs a couple of large cores with multiple instructions like the CPU.)
CUDAs main strength is that it makes programming a lot easier for devs, at the cost that its implementation is black box and proprietary. when you have devs use such a proprietary language, the it makes it significantly harder to jump ship if your work relies on it to make a profit.