open angle brackets in Linear Algebra

Question

I know that $\langle v,w \rangle$ denotes the scalar (inner) product of two vectors. But how to interpret $I = | 0 \rangle \langle 0 | + | 1 \rangle \langle 1 | $, where is (I think) the identity matrix and $\sigma_x = | 1 \rangle \langle 0 | + | 0 \rangle \langle 1 |$ the Pauli X matrix?