CISC - complex instruction set - you'll get really exotic operations, like PMADDWD (multiply numbers, then add 16-bit chunks) or the SSE 4.2 string compare instructions
RISC - reduced instruction set - instead of an instruction for everything, RISC requires users to combine instructions, and specialialized extensions are fairly rare
Modern CISC CPUs often (usually? Always?) have a RISC design behind the CISC interface, it just translates CISC -> RISC for processing. RISC CPUs tend to have more user-accessible cores, so the user/OS handles sending instructions. CISC can be faster for complex operations since you have fewer round-trips to the CPU, whereas RISC can handle more instructions simultaneously due to more cores, so big, diverse workloads may see better throughput. Basically, it's the old argument of bandwidth vs latency.