What does it mean when a bank is nationalised?

[twinkletwinklepops]

Hi there - can someone help me understand what it means when a bank is nationalised.
The bank that I have my mortgage with has just been nationalised and I want to know if I need to do anything.
They've set up a Helpline for customers so I wondering if I need to be concern by this nationalisation?? Is there any impact on me or does it just mean the state is now the sole shareholder.
I live in holland.

Thank you.

[BeforeAndAfter]

You're right - it means the government/tax payer owns either all or most of the bank's shares. Your mortgage should be fine but call the help-line and get all of your questions answered.