Noun
daughterboard (plural daughterboards)
(computing, electronics) A circuit board that is an extension of a motherboard or other card.
Synonyms: daughtercard, mezzanine board, piggyback board
This came in 1995, as an Apple Motherboard containing a 100 MHz 603e processor and 8 MB of RAM (which snapped into a slot containing the previous 25 or 33 MHz 68040 processor and the 4 MB of RAM on the previous daughterboard). Source: Internet
The power supply was marginal, and some would overheat if the system memory was expanded to the full 512 kB capacity due to the considerable heat generated by the additional RAM on the optional daughterboard. Source: Internet