"Extra slack" means having additional leeway or flexibility beyond what is normal or expected. It refers to having more time, freedom, or resources available to deal with unexpected situations or to relax. Full definition
In other ways, it's a good idea to cut family members a little extra slack. (thespruce.com)
This leaves the upper body unprotected and adds extra slack into the seat belt system, putting your child at risk of severe injury in a crash or with sudden braking. (healthychildren.org)
This leaves the upper body unprotected and adds extra slack to the seat belt system, putting your child at risk of severe injury in a crash or with sudden braking. (twiniversity.com)