What process involves a product or service starting in simple forms and eventually moving "up market" to displace established competitors?

Disruptive innovation is the correct answer as it describes a process where a product or service begins with basic characteristics and initially targets a niche market. Over time, as it improves and gains traction, it expands its appeal to more mainstream customers, ultimately leading to the displacement of established competitors.

This concept was introduced by Clayton Christensen and illustrates how smaller companies can successfully challenge larger, established firms by offering simpler, more affordable, or more convenient products. These innovations often start off seeming inferior in performance or capability when compared to existing solutions, but they gradually evolve and can outperform established competitors by meeting unmet consumer needs.

In contrast, incremental innovation refers to small, gradual improvements made to existing products or services rather than a fundamental change that can disrupt a market. Radical innovation involves breakthrough ideas that can create entirely new markets or industries, but may not follow the same trajectory as disruptive innovations. Continuous improvement focuses on ongoing enhancements to processes and products while maintaining existing values, rather than moving "up market" to challenge competitors directly.