the state of being slower and less active than usual

Low sales figures were partly because of normal mid-summer slackness in/of demand. 销量不高一部分是由于仲夏时节正常的需求不旺造成的。

the fact that a person or organization is not working as well or as hard as they should

The inspector criticized the slackness and incompetence of the staff. 巡察员批评了员工的懒散和无能。

the state of not being tight