Almost all the definitions I've found state the following:
TOP DEFINITION
Squib load
A defective round of ammunition that lacks sufficient power to force the projectile out of the barrel of a firearm.

Indicators of a squib load may include: little to no recoil, gasses directed back toward the shooter, or failure to cycle another round.

If you experience a squib load, point your firearm in a safe direction, and ensure that it is unloaded. Use a cleaning rod to push the projectile out of the barrel.

Never attempt to fire another round to force the stuck projectile out. This will create pressures that your firearm is not designed to tolerate, and will damage your firearm, and likely result in injury or death.

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GreyOwl