It means someone has stolen details of your card and bank has blocked it.
Before you use your credit card online and offline, make sure of the following things
1) Your computer is free of any spyware, keylogger software etc.
2) Only shop from your personal computer, never from someone else's computer
3) Shopping offline, never leave you card with the shopkeeper, always keep it in your sight
In my opinion every credit card should have a secret pin code like debit cards. The transaction should only be processed if the user enters the correct pin code. This simple step will prevent credit card fraud. I don't know why banks don't implement it.