Core file eat my space!!

Disk Usage Warning full
The account with the username 'xxx' (sasidesign.com), is running out of disk space.
Please remove some files from this account, or ask the administrator to increase your disk quota.
This account has used 100.02% (120.02 Megs) of its allocated disk space.
!! Do not respond to this message. Your reply will go nowhere. !!

and i go to check it up on in my public_html than find file core.2323 till 20mb and 30mb, thats why my disk was full, and i deleted all file named core.. than my hosting was no full again.
but i still didnt understand why that file can in at my hosting..

somebody know?