It's a term I'd never heard before reading here
Basically it's when far too much detergent is used so that when the machine tries to spin, thick foam clogs the pump and gap between the tubs, causing suds to overflow out of the gap between the tubs and flow down the glass.
This results in huge strain on the motor, and I would imagine will do the bearings no favours, so they are certainly best avoided if you want to keep your machine in good condition.
Damage to the machine aside, if the machine dosen't clear the "sudslock" by the end of the spin, none of the detergent or water is really removed during the spin and a thick layer of suds is dumped into the next rinse, giving extremely poor rinse results.
I've pretty much got my doses now so that this never happens for me. On a rare occasion it does happen, if the machine dosen't cut out automatically due to the strain on the motor being too great, I stop the machine and make it repeat the spin until all the suds are removed so that rinse performance isn't compromised.
Matt