Hi. I do not understand what "liable to damp off" ; "prevent damping off" is as in below. Can anyone explain ? Thanks.

 

Over watering can cause a root fungus that kills plants. We called it Root Rot. I've never heard it called damp off (off, normally used as slang for killing a person or thing).
https://hort.extension.wisc.edu/articles/root-rots-garden/

 

damp off, damping off disease - a disease caused by cold, wet conditions, that kills young plants that are just starting to grow from seed, usually caused by over-watering and poor drainage and air circulation.