Whether or not you can hear people scream in space, there’s plenty of screaming, or at least disagreement, about space and the way we describe it.

So much so, in fact, that California’s SETI Institute – the acronym stands for Search for Extraterrestrial Intelligence – felt the need to convene an Ad Hoc Committee on SETI Nomenclature to make a few decisions on definitions. The committee included astronomers Jason Wright and Sofia Sheikh from Penn State University, US, and distinguished researcher Ivan Almar from Hungary’s Konkoly Observatory.

The resulting recommendations, which are available online, make interesting reading, starting with what can only be described as a bit of a disclaimer.

“This is a consensus document that the committee members all endorse; however, in many cases the individual members have (or have expressed in the past) more nuanced opinions on these terms that are not fully reflected here,” the document says.

Then follow nine pages with 24 terms defined, ranging from the simple (alien, intelligence, extraterrestrial) to the complex (Schelling Point, Fermi Paradox, Drake Equation) to the acronym-heavy (CETI, SETA, METI, Active METI, Artifact SETI).

Starting at the top, SETI as a noun is: “A subfield of astrobiology focussed on searching for signs of non-human technology or technological life beyond Earth. The theory and practice of searching for extraterrestrial technology or technosignatures.”

Extraterrestrial is defined with the rider that the terminology is complicated by the interplay between Earth and the wider solar system, while alien is defined but not loved. It is to be avoided as a noun and is not even recommended as an adjective. Definitions of intelligence are “slippery and much broader than technological”.{%recommended 7383%}

Based on the agreed definitions, natural and artificial seem pretty straightforward, but even here there is a note referring to slipperiness because they are “not even well defined for observable phenomena on Earth”.

We’re in clearer air with beacon: “Any ‘we are here’ sign or signal deliberately engineered by a technological species to be noticed, recognised, and understood by another technological species as evidence or proof of the first technological species’ presence.”

A dial tone or door bell is a “content-free beacon” – as in ‘we’re here, but with nothing to say at this time’.

Settle or colonise are pretty clear, but the committee notes that some shy away from the latter term because of connotations of the global exploits of European powers in past.

Few out-and-out disagreements are revealed, which is probably what nuanced consensus brings. However, there are strong suggestions that certain terms are not well regarded.

SETA, for example, which stands for Search for Search for Extraterrestrial Artefacts, for example, is “deprecated” because it should be considered a subset of SETI rather than a distinct activity, while METI – Messaging Extraterrestrial Intelligence – is straight out “controversial”.

“Some consider it to be logically continuous with SETI, and others consider it to be a distinct activity,” the authors write. “To some it also includes replies to future hypothetical incoming transmissions, and theoretical work on how to communicate with ETI, but others consider these to be distinct from METI.”

In contrast, Kardashev Scale, Fermi Paradox, and Drake Equation all appear uncontroversial, with a definition and some guidance on usage provided.

For those planning a SETI discussion in the near future, note that Schelling Point (“an equilibrium in a non-communicative cooperative game such as a mutual search”) is considered to have “priority over and is to be preferred to terms in the literature that have not caught on such as mutual strategy of search, synchrosignals, or convergent strategy of mutual search”. So there.

Also, Rio 2.0, a proposed update of the Rio Scale (which was developed by astronomers to express their estimates of the importance of a report of detection or contact with an extraterrestrial species) has not been adopted by the International Academy of Astronautics and so currently has no official status. It would be useful to remember that, the next time subject arises over the dinner table.