What is gerrymandering and how has it influenced elections?

To “gerrymander,” pronounced with a soft g, is a verb derived from the surname of Elbridge Gerry, pronounced with a hard g. While he served as governor of Massachusetts, Gerry’s administration in 1812 passed a law that revised the state’s senatorial districts. The new boundaries ensured disproportionate representation of voters for one party, virtually guaranteeing that its candidates would be elected. The shape of the new districts was compared to that of a salamander, and thus the word "salamander" was combined with his name (a portmanteau coinage) to produce "gerrymander."
The term “gerrymandering” has thenceforth been applied in the United States to the process of redrawing any kind of political district boundaries. One negative effect of this practice is that the resulting size and composition of districts is profoundly unequal. As this type of selective redistricting tends to favor one candidate within a specific district, often according to race as well as political party, it effectively discriminates against minority candidates. In extreme situations, when a number of individual districts are combined throughout a state, it can mean that a candidate with the most votes overall still loses, because the majority takes each individual district. On the other hand, when a district is drawn to include primarily people who constitute minorities of nearby districts, it can be a means of guaranteeing one representative for that group.
https://www.britannica.com/topic/gerrymandering