SPD - Serial Presence Detect: memory modules communicate their capacity and features to BIOS at start up.
Your memory modules may need some intelligent input for them to run at their rated speeds. SPD is a memory hardware feature that makes it possible for the computer to know what memory is present, and what timings to use to access the memory. The SPD speed and the rated speed are probably different so you may need to input the rated speed settings, timings and DRAM voltage for the memory to work correctly. The SPD timings are usually good enough to get the machine started for you to input the changes in the BIOS.
You may want to run CPU-Z and click on the SPD tab and see if you come up with the part number of the memory. The rated speeds are usually also printed on the memory label itself.
Intel uses extreme memory profile (XMP) which requires minimal BIOS configuration and is supported by the newest chipsets. There are predefined and certified memory optimizations built into Intel XMP. This simplfies the BIOS memory setting process, but nevertheless the setting would need to be enabled if your motherboard uses XMP.