This is a common acronym used in the Lego community - what does MOC mean?
MOC stands for "My Own Creation".
My Own Creation. Any LEGO creation designed and built by a LEGO fan without instructions. Generally pronounced “mock.”*
Found at this Lego glossary.
Brickipedia's version from their own glossary:
MOC - My Own Creation, a fan- made LEGO model
*A side note: There may be some LEGO fans who pronounce "MOC" the way the individual letters are pronounced - effectively saying "Em-Oh-See".