In less abstract and wonky terms, it's when you change laws in ways that benefit you directly but harm others who have to use what you're providing. Examples of rent-seeking occur in the beer industry where "regulation capture"--another beautiful term from the literature--restricts, I believe, the sale or transport of beers into states. The people who have established oligopolies within a particular state have access to the market whereas other smaller breweries have difficulty to making inroads on that market.
Deaton is talking about the legislation and policies that health care and finance are introducing that protects them from competition with the knowledge that others will still need to use their services. Usually, this sort of rent-seeking is done under the justification that it provides quality control over goods and services being provided which is, to be fair, sometimes the case or atleast a possible outcome. More often than not it is preserve advantages and create barriers to entry to prevent competition from eroding revenue and, of course, margins.
It's only business school that you learn about the powers of competition. In reality, businesses hate competition and they'll do whatever they can to prevent it from entering. Rent-seeking describes how that occurs.
Land rent is the original example of rent seeking. SV rents would probably qualify, since the cost of rent in SV is more connected to the land and location, as well as the regulations on that land, versus the improvements on the property. Maybe $4000/mo of your rent is based on "rent-seeking" and $1000/mo is based on the property itself.
Looking for example at Silicon Valley, it's easy to see that rental property owners are sucking large amounts of wealth out of the region. It's not just rental property, though. Anyone who bought a house prior to the recent run-up in prices, and then sold it for a large gain, is effectively also removing wealth from the area, in the form of the mortgage payments the new owner has to pay.
George argues that wealth that is collectively created should be collectively enjoyed, and that the best way to make that happen is through a Land Value Tax (LVT) -- that taxes only the unimproved value of land, not that of any structures that may be built on it.
$5000 on rent is absurd. Wow!
From Wikipedia, a feudal lord puts a chain over a river and charges a toll to lower the chain. No value add, just money in the pocket of the lord.
And the contemporary version: an investment firm buys out the intellectual property of a medical delivery device. They charge additional royalties to the manufacturers of the device. No value added.