Raising to the T in machine learning What does it mean when in a machine learning paper there is
$(arg)^{T}$, what does the T does to an arg  in this 3b1b video on neural networks he puts the: $(w^{l-1})^{T}$
The notation $A^T$ stands for the transpose of a matrix. It is not specific to machine learning, but rather standard notation in linear algebra. Other notations are sometimes used, for example $A'$.
A related operation is the adjoint $A^*$. The transpose and adjoint are equal for real matrices.