not taut or held tightly in position; loose

a slack rope

her mouth went slack

(of business or trade) characterized by a lack of work or activity; quiet

business was rather slack

having or showing laziness or negligence

slack accounting procedures

lewd

the veteran king of slack chat

(of a tide) neither ebbing nor flowing

soon the water will become slack, and the tide will turn

slack tides

a person who avoids work or effort

the slackers who let the side down by their want of team spirit

a young person (especially in the 1990s) of a subculture characterized by apathy and aimlessness

they are portrayed as dreamy, disenfranchised slackers

slacker culture