Final answer:
Tier three Internet Service Providers connect end users to the Internet by purchasing connectivity from higher-tier ISPs. They are typically local companies that serve households and small businesses and are implicated in debates surrounding net neutrality and the digital divide.
Step-by-step explanation:
An Internet Service Provider (ISP) that qualifies as a tier three provider is typically the last link in the Internet access chain, connecting end users to the larger networks operated by higher tier ISPs. Tier three ISPs are often local businesses providing Internet services directly to households and small businesses. These providers typically purchase Internet connectivity from tier one or tier two networks and then sell this connectivity to their customers. They may not have their own expansive infrastructure and hence they rely on the higher-tier ISPs to access the broader Internet.
In the context of net neutrality, a tier three ISP might be affected by regulations and policies that govern how Internet traffic is treated. Net neutrality advocates argue that ISPs should treat all data equally, without giving preferential treatment to certain services or charging more for higher-tiered delivery, which could affect tier three providers and their customers. The debate on net neutrality also touches upon the importance of ISPs in contributing to the digital divide by potentially creating inequalities in Internet access and service quality.