Dynamic IP keeps on changing every time you connect to your ISP (internet service provider) so let say you want to host some website on your local computer then you will be needing a static IP that will not change or else if everytime the IP changes your site will not work.
Each has its own advantages or drawbacks. If let say one site blocks you based on IP from accessing it then you are stuck and can't access that site with static IP, while if your IP changes the next time you can connect to the same site without any problems.
