# Spaceship terminology

There are many different **terms** used when describing specific aspects of spaceships in Conway's Game of Life and related cellular automata. The following are the terminology that are in common use. This page contains only very general terminology that applies to wide varieties of spaceships.

## Arm

An **arm** is a long extension hanging off from the main body of a spaceship (or puffer) that is perpendicular to the direction of travel. Many known spaceships have multiple arms. This is an artifact of the search methods used to find such spaceships, rather than an indication of what a "typical" spaceship might look like.

## Edge spark

An **edge spark** is a spark that appears at the side of a spaceship that can be used to perturb things as the spaceship passes by. For instance, a heavyweight spaceship produces a domino edge spark that can be used to perturb or eat things.

## Heat

*Main article: Heat*

The **heat** of a spaceship (or oscillator) is the average number of cells that change state in each generation. For example, the heat of a glider is 4, because 2 cells are born and 2 cells die every generation.

## Mod

*Main article: Mod*

The **mod** of a spaceship (or oscillator) is the least number of generations that it takes for it to reappear in its original form, possibly reflected or rotated in some way.

## Period

*Main article: Period*

The **period** of a spaceship is the smallest number of generations that it takes for it to reappear in its original form, translated by a non-zero amount.

## Speed

*Main article: Speed*

The **speed** of a spaceship is a measure of the number of generations that it takes for it to travel some given distance.