A dedicated IP address refers to web hosting or email platform services.
In web hosting context, a dedicated IP address is the same thing that a dedicated server. By accelerating loading times, it may favorably impact user experience, SEO and SEA.
In email marketing context, dedicated IP address means that a server is specifically and exclusively dedicated to a company by an ESP (email service provider).
A dedicated IP address allows the ISP customer to control his sender reputation and favors a better deliverability through better IP and domain reputation. It also allows complying more easily with some email authentication protocols.
Dedicated IP address is usually advised for companies managing at least 20 000 subscriber lists. New dedicated addresses need "warming up".