pouring one's own drink; helping oneself to a drink
Refers to pouring a drink for oneself, especially in a social drinking context where it is more common for others to pour for you. Often used in the phrase 手酌酒.
He always pours his own drinks.
At banquets, people don't often pour their own drinks.
Compound of 手 (hand) and 酌 (pouring sake). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning of self-service in drinking.