# Norm type in cost function of ANN

I'm reading a tutorial about ANN. They use the following cost function:

As you can see this equation includes a norm. I'm new to the concept of norm.

My question is what kind of norm they use here (There are Absolute-value norm, Euclidean norm, Euclidean norm of a complex number, Taxicab norm, Manhattan norm, p-norm, Maximum norm, infinity norm, uniform norm, supremum norm, Zero norm, etc.)

The two vertical lines represent the $$L^2$$ norm of the error, or what is known as the sum-of-squares error (SSE)
Otherwise known as the Euclidean norm, Euclidean length, $$L^2$$ distance, $$ℓ^2$$ distance, $$L^2$$ norm, $$ℓ^2$$ norm, $$2$$-norm, or square norm.