The word "slackness" refers to a state of being lazy, lacking effort, or not being strict or disciplined enough. It can also indicate a lack of tension or tightness in something. Full definition
With Tooth's turtle posture and the utter slackness of his being, his receding hairline and antique manner of dress — trim - tapered suit, ferociously wrinkled silk with the shine worn off, moldering tennis shoes — I could have taken him for elderly. (bookbrowse.com)
And secular, for Catholics, meant a certain slackness in moral and academic discipline. (educationnext.org)
Past managers such as George Graham, whose trophy haul was 6 in 9 years, compared to Wenger's 10 in 21, never stood for slackness, laziness and was ne ver afraid to drop out of form players or ones who just didn't cut the mustard. (justarsenal.com)