static IP means the IP address always stays the same. Some ISPs will automatically give a business account one, others will charge for it.
dynamic IP means the IP address changes (sometime it may be daily, sometimes you might have the same IP for an extended period of time). Usually you can 'force' getting a new IP by restarting the ISP's modem (not your own Linksys, Dlink, etc...the other box you have). After doing this, you may need to restart your own router as well.
Is that clearer, or do you still have questions?