Silo phrases explained: All the key terms you need to know

From the Before Times to cleaning

Silo

Author: Anna Sky MagliolaPublished 22nd Jul 2026
Last updated 22nd Jul 2026

Silo season three is hitting our screen this summer through a weekly release of episodes and we're creating a full recap of the series episode by episode, right back from season one, episode one.

Silo, set predominately in 2352, has a set of terms that you will only find in the series (based on the Silo series of books - Wool, Shift and Dust), written by American author Hugh Howey. Here we take a look at what the terms mean...

WARNING: SPOILERS BELOW

What do these Silo terms mean?

Going out to clean

Going out to clean in Silo its basically a death penalty. Residents of the Silo who go out to clean don't come back alive. They are sent out for two reasons, either because they break the law or they ask to go out voluntarily.

When they are outside, they clean the lens on a camera that displays on the screens in the cafeterias. Over time the lens gets covered in dust and debris from the toxic wasteland the residents of the Silo can see.

SPOILER! (Juliette is the only person so far to come back alive)

Up Top

The Silo consists of 144 levels, and they are connected by a single spiral staircase, there are no lifts. It is split into three main sections. Up Top is where the primary government offices, the Sheriff's station, and the surface airlock are situated.

The Mids

Below Up Top is The Mids, where many of the residents live along with the schools, and The Farm that grows food for the population. It also houses the Mids Medical, where Juliette's dad, a doctor, oversaw the nursery.

Down Deep

At the bottom of the Silo is the Down Deep. The people who live down there and keep the generator going rarely go up to The Mids or Up Top. There are many Deputy stations throughout the Silo, but the Down Deep Deputy Station is where Deputy Hank Murphy is charge. He is good friends with Juliette and Knox who work on the generator.

The Mines

Being sent to the mines is seen as a punishment for those who break the law. Iron ore was mined from The Mines, which are dirty and full of rats. Lukas Kyle is banished to The Mines for not reporting Juliette's relic.

The Digger Void

The area around the digger that was used to build the Silo is called The Digger Void. In the Digger Void is a camp made by George, where he hides a few relics, later Bernard is found hiding there, after many believed he had died.

Shadow

Someone's shadow is like their deputy, they are expected to learn from their mentor. In one of the early episodes Juliette gets a shadow called Terry Cooper. Juliette was previously Knox's Shadow, when she first transferred from The Mids.

The Algorithm

A select few from the Silo ever encounter The Algorithm, a voice that speaks to certain people about the Silo in a bright room with stepped walls. Although the subtitles call this voice The Algorithm it isn't referred to by the characters as such, and many don't know of its existence.

The Farm and 'going to the farm'

The Farm refers to the many farms in the Silo, where they grow crops and have animals such as pigs and chickens for the 10,000-strong population.

However, there's a slightly grim feature of The Farm, when members of the population die they can be buried in The Farm, so that their body's nutrients helps to feed the crops.

Before Times

Before the Silo was built was the Before Times - set in the near future (2040s). Not much is known about the Before Times in the first two seasons, with the third season beginning to explore why the Silo was created.

Judicial

Similar to the Sheriff, Judicial help to keep law and order in the Silo, they are responsible for enforcing The Pact and confiscating any relics.

Relic

Something from before the Rebellion. It's illegal to be in possession of a relic and knowing that someone has one and not reporting them can also be a punishable offence.

The Pact

The Pact is a book that the rules of the Silo are set out in. Several characters refer to The Pact throughout the series and how they must follow the rules.

The Rebellion

140 years before Silo is set there was a Rebellion when the residents of the Silo stormed the upper levels wanting to open the door to the surface and poison the entire Silo with air from outside. The Rebels burnt all the books, computer drives and anything from the Before Times.

Safeguard

A hidden pipe system which can flood the Silo with toxic gas. Use of it is designed to end the entire Silo's existence, but it isn't controlled by Silo 18, instead it is controlled by the overseers of Silo 1.