Austin Kleon said,

Creativity is about connections, and connections are not made by siloing everything off into its own space. New ideas are formed by interesting juxtapositions, and interesting juxtapositions happen when things are out of place.

your beachhead is the smallest customer segment you can target that serves as a point of attack into the main market you want to break into. This niche has a set of characteristics that make it an ideal place to focus your initial effort.