Political Memes

Wikipedia defines it well, with some history of the term

The petite bourgeoisie is economically distinct from the proletariat and the Lumpenproletariat social-class strata who rely entirely on the sale of their labor-power for survival. It is also distinct from the capitalist class haute bourgeoisie ('high' bourgeoisie) that owns the means of production and thus can buy the labor-power of the proletariat and Lumpenproletariat to work the means of production. Although members of the petite bourgeoisie can buy the labor of others, they typically work alongside their employees, unlike the haute bourgeoisie.

Here is another two definitions from marxist.org's glossary of terms: https://www.marxists.org/glossary/terms/p/e.htm

1. The class of small proprietors (for example, owners of small stores), and general handicrafts people of various types.

This group has been disappearing since the industrial revolution, as large factories or retail outlets can produce and distribute commodities faster, better, and for a cheaper price than the small proprietors. While this class is most abundant in the least industrialized regions of the world, only dwindling remnants remain in more industrialized areas.

These people are the foundation of the capitalist dream (aka “the American dream”): to start a small business and expand it into an empire. Much of capitalist growth and development comes from these people, while at the same time capitalism stamps out these people more and more with bigger and better industries that no small proprieter can compete against. Thus for the past few decades in the U.S., petty-bourgeois are given an enourmous variety of incentives, tax breaks, grants, loans, and ways to escape unscathed from a failed business.

2. Also refers to the growing group of workers whose function is management of the bourgeois apparatus. These workers do not produce commodities, but instead manage the production, distribution, and/or exchange of commodities and/or services owned by their bourgeois employers.

While these workers are a part of the working class because they receive a wage and their livelihood is dependent on that wage, they are seperated from working class consciousness because they have day-to-day control, but not ownership, over the means of production, distribution, and exchange.