Pre existing conditions for pet insurance is any condition, disease or illness that your pet has or had before you purchased the pet insurance policy.
Most pet insurance policies do not cover any pre existing conditions or illness prior to you purchasing pet insurance.
The pet insurance policy will only cover any conditions or illness that occur after you take out the pet insurance but you usually must wait from 48 hours to 14 days before you can claim on a pet insurance policy.
Also usually you have to pay out of pocket for the vet bills and then wait on the pet insurance company to reimburse you for those costs.