Refers to drinking alcohol at one's own home, often in contrast to going out to bars or restaurants. Similar to 家飲み (いえのみ).
See also: 家飲み
Lately, I've been drinking at home more often.
It's also fun to invite friends over and drink at home.
Compound of 自宅 (one's home) and 飲み (drinking, nominalized form of 飲む).