It's mapping out districts so they only vote Republican.
Most republicans are in rural areas, most democrats are in cities.
So, they map out a district that is mostly rural, and, with only a small city, so as a whole it will vote the way they want.

Very common in Oz, I grew up under such a system.
From 1948 until the reforms following the end of the Bjelke-Petersen era, Queensland used an electoral zoning system that was tweaked by the government of the day to maximise its own voter support at the expense of the opposition. It has been called a form of gerrymander, however it is more accurately referred to as an electoral malapportionment. In a classic gerrymander, electoral boundaries are drawn to take advantage of known pockets of supporters and to isolate areas of opposition voters so as to maximise the number of seats for the government for a given number of votes and to cause opposition support to be "wasted" by concentrating their supporters in relatively fewer electorates.

It has been around for a long time and both parties do it. The Democrats did it back after they lost the civil war up to the time that they became all inclusive and changed their platform. The old members that did not like that change left and joined the Republican party, and enacted the southern strategy during the civil rights movement and continue to use it today.

I grew up with this:

[chron.com]

It's terrifying that there are people that don't know about this. Spread the word.

Gerrymandering came about by combining different voting districts state wide by the dominate Political party in power to retain it's grip on power. It was first used by Govenor Gerry of Massachusetts. I believe he was a Dem.
Another 1st in the nation by My state..

It’s a bad word… For a long time both parties would ‘nudge’ various voting districts one way or another, kind of a trade-off … especially in Oregon; I watched. But as they do, the Republicans weaponized the process, similar to their recently detonating the ‘nuclear option’ in the US Senate…

How’s Gerrymandering affect me now? In my SW VA congressional district a major liberal college has been ‘carved out’ and added to the nearest large liberal city. So, the ‘city district’ becomes more progressive - as ‘my district’ becomes less competitive and more regressive ...as ‘my congressman’ reflects..

The nation needs a fair makeover regarding political districts and boundaries, problem is, the ones who’ve benefited from them ‘as drawn,’ are not about to allow that… And the few judges/ courts willing to force it, are currently being flooded with ‘trump judge appointments’ who’ll see no problem with the current system -- as it’s the very system that allow their benefactor to ‘win’ and for them to ‘be seated’ (6)

Gerrymandering is a long-standing practice. I've lived in several states where it has been practiced. It's also part of what got 45 the Electoral College vote. Anytime there is Congressional redistricting, people really need to be paying very close attention. Most don't, but they need to.

I'm in Texas. It's a huge problem. Some states have started using non partisan commissions to take it out of the hands of the politicians.

Both Democratic and Republican politicians and parties have used gerrymandering before to create an unfair political advantage the "stack the deck." But, today, Republican gerrymandering in states now controlled by Republicans at the state level that they are trying to create a stranglehold which will keep them in power for a long, long time. It has poisoned our politics at all levels -- local, state, and national.

Trump

It is just a political way to rig an election in your political party's favor. Both parties do it but the GOP seems to have made it their mission to maintain power in their control any way they can. (IMHO)