Slack is the collaboration hub, where the right people are always in the loop and key information is always at their fingertips. Teamwork in Slack happens in channels .Slack is where work flows. It’s where the people you need, the information you share, and the tools you use come together to get things done..Slack slk adj. slacker, slackest . Not tense or taut loose a slack rope slack muscles. See Synonyms at loose. . a. Lacking in activity not busy a .Slack APIs allow you to integrate complex services with Slack to go beyond the integrations we provide out of the box..