"Sterilised" fields and SQL injection

Hey,

I’ve recently started designing a WordPress site for a client who has their own server. The server guy I’ve been talking to says I need to make sure “all fields submitted to the site are sterilised before entry into the database” so we don’t get anyone trying “SQL injection”.

To be honest I’ve no idea what this means. I’m mainly a designer so I’m not so hot on the development stuff.

Can anyone help? Has WordPress got this covered or is there something I need to do?

Thanks,
Sam