In a Facebook thread about Amtrak trains I saw a user comment complaining about Amtraks cattle call seating policy.
What is this?
This is a US term meaning that seats are not pre-booked but grabbed on a first-come first-served basis.
The term originated with Southwest Airlines, which was the first airline to eschew seat assignments at booking or confirmation time (or at least the first well-known airline in the US). Here's an early use of the term from 2001:
The "cattle-call" seating policy on Southwest has its downside, which is competition with your fellow-passengers for an early boarding pass. By now, most people are familiar with Southwest's policy for seat assignments -- they don't have any. You just walk on board the plane and pick the seat you want as long as it isn't taken. The first person to check in gets a boarding pass with a "1" on it, the second person a "2," and so on.
In other words, passengers choose their own seat, and they get to choose in a first-come, first-served basis.
After a few years, Southwest changed their policy to allow passengers to reserve a seat in advance, for a fee.
Starting in early November, customers of Southwest Airlines Co. will be assigned a letter-number combination on their boarding passes, which will reserve their spot in their boarding group. According to a Southwest statement, when a gate agent calls a boarding group, passengers will take their place in their numerical order.
However the term “cattle-call seating policy” has remained in use even Southwest no longer practiced the “cattle call at the gate” approach where everyone in the terminal would scramble to be first in line. The cattle call changed to a scramble to be the first to check in online¹ to get a higher boarding priority.
Today the term is used to mean a first-come, first-served seat assignment policy, i.e. no booked seats. It is occasionally used outside air travel, e.g. about cinemas:
And once all the reserved seats are gone it’s back to general admission otherwise known as the cinema cattle call.
¹ Which is the case on most airlines anyway.
Other answers already have connected to the practice of some airlines of not assigning seats but just calling groups of passengers (or sometimes everyone) to join and grab whatever seats are available.
The phrase "cattle call" actually comes from the theater world, where it referred to open auditions, although sources differ whether the usage was started by actors feeling disrespected by the process, or by producers and directors disgusted with the stampede of ambitious actors.
But "cattle call" originated with 19th-Century ranchers and cow-hands, who would literally call out chants ("Co-bessie, co-bessie, co-bessie!" and "Co-wenchie, co-wenchie, co-wenchie" were popular, "co" meaning "come") to summon cattle to feed.
Cows are surprisingly easy to train in this way. A rancher friend of mine was in the habit of riding his motorcycle around his land and throwing cubes of alfalfa to his cattle. Soon, anyone on a motorcycle would find himself thronged by copiously drooling cows.