In a Symmetric Multiprocessor, the architectural “distance” to any memory location is the same for all processors, i.e. “symmetric”.
In a NonUniform Memory Access machine, each processor is “closer” to some memory locations than others; i.e. memory is partitioned among them Asymmetrically.
From my understanding, most of current architectures are SMP+UNMA if we consider cache is also part of memory hierarchy.
Part of above answers are copied from https://www.quora.com/What-is-the-difference-between-SMP-and-NUMA-architectures