This is the colloquial term for when the extruded filament builds up around the hot end in a huge blob.

This is always caused by conditions created through owner/operator error.

Klipper relies on the extruder rotational distance value to calculate the amount of filament that needs extruded. If the value wasn't properly tuned, the extruder can over extrude material.

Extruded filament curls and leaks around the nozzle due to the filament profile not properly calibrated along with improper retraction setting coupled with too hot extruder temperatures.

Default filament profiles are not really designed other than as a starting point for your own calibrations. Each filament you use needs properly calibrated. When the filament isn't properly calibrated it can over extrude out the nozzle. These over extrusions curl around the nozzle and build up.

Over extrusion, bad gantry alignment, bad infill or other issues cause the part to get knocked from the plate and caught on the nozzle, resulting in it getting dragged around and the following extrusions build around the knocked part which wraps around the hot end.

Solve part knock issues. Calibrate the filament properly, align the gantry, use infill that doesn't require crossing already extruded lines in the same layer. (e.g. no grid infill)

If the nozzle was replaced and not seated properly molten filament can leak through wear the nozzle and hot end meet.

If there's too much back pressure in the upper part of the hot end and it's not well seated the molten filament can leak through the upper part of the extruder.

Properly seat the nozzle and hot end.