OCA
OCA is an acronym for "other cellular automata". This includes Life-like CAs, isotropic CAs, anisotropic non-totalistic CAs, rules with more than two states, rules that operate on non-square grids or with neighborhoods other than the Moore neighbourhood, and every other type of cellular automaton that is not Conway's Game of Life.
Notable non-Life rules, when they are catalogued on the LifeWiki, have article names prefixed by "OCA:" -- e.g., OCA:HighLife. When these rules support notable patterns that have their own pattern pages, these are stored as subpages of the rule page -- e.g., OCA:HighLife/Bomber.
Alien
Alien, in the context of Conway's Game of Life, denotes concepts not related (i.e. alien) to Conway Life. The term is primarily applied to rules and patterns. An alien rule is any cellular automaton other than Conway Life itself; an alien pattern or alien object (sometimes shortened to "an alien") is a pattern or object not existing, or behaving differently, in Conway Life.
For example, Day & Night (B3678/S34678) is an alien rule; the fireball, a period-40 spaceship in Day & Night, is an alien spaceship:
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