дОма 1 - stress on O is an adverb, not a regular case form. Yes, as Abai pointed out it's 'at home' дОма 2. - genitive, 'of a house', домА - (stressed A) - houses.

Capital letter denote stress: Sg. nom. дом gen. дОма dat. дОму acc. дом instr. дОмом prep. дОме pl. nom. домА gen. домОв dat. домАм acc. домА instr. домАми prep. домАх related adverbs: дОма (at home) домОй ([verbs of movement +] home)

Дом -home For Example:sweet home,милый дом Дома - at home For Example: I sit at home

Дом - singular дома - plural It is exception in Russian language .