Rank: 1 (pure outer product)
u⊗v = uvᵀ (outer product). A matrix M has rank 1 iff M=u⊗v for some vectors. The SVD M=UΣVᵀ decomposes any matrix into sum of rank-1 tensors. In quantum mechanics, |ψ⟩=|a⟩⊗|b⟩ means the state is separable (not entangled).