Any specialised activity has its own vocabulary, and fiction about it has to decide how much of that vocabulary to use. Too little and the work sounds like it was written by somebody who has read about the subject; too much and readers outside the field stop following. There is no correct amount, only a decision that has to be made deliberately.

The decision is usually made by default, which is where problems come from. Writers steeped in a subject overuse its terms without noticing, and writers who are not risk using them incorrectly, which is worse.

What vocabulary buys

Precision, first, since a specific term describes something a general phrase cannot. Authenticity, second, because readers who know the field recognise correct usage immediately and relax. And characterisation, since who uses which terms says something about experience and about how each person relates to what they are doing.

That last one is the most useful and the least exploited. A character who uses precise vocabulary and one who describes everything in ordinary words are characterised by the difference, and the contrast is available for free in any scene with two people.

What it costs

Readers who do not know the terms are excluded, and exclusion in the middle of a scene is worse than exclusion at the start because they were engaged and are now stopped. A page that requires a glossary is a page most readers will skim, and skimming is where a carefully built scene loses its effect.

There is also an authenticity trap. Terms used slightly wrong signal the opposite of expertise to exactly the readers who would have appreciated it, which is the borrowed-tradition problem set out in the piece on borrowed rope traditions.

Define through context

The only comfortable way to introduce a term is through context, where what is happening makes the meaning obvious and the word attaches to it. A character does something, another names it in passing, and the reader has learned a word without being taught one.

The alternative, a character explaining terminology to another character who would already know it, is the exposition failure described in the piece on writing two-handers. Readers detect it instantly and it damages the scene it was meant to support.

When to describe instead

If you are not confident a term is correct, describe what is happening instead. Plain description is never wrong, always readable, and frequently more vivid than a technical name, which compresses something into a label the reader has to unpack.

This is the same recommendation made about labels generally in the piece on reclaimed words. Description costs a few more words and eliminates an entire category of error.

Density changes by scene

Vocabulary can be dense in a scene about preparation or negotiation, where naming things is what the characters are doing anyway, and sparse in a scene where the reader should be following feeling rather than technique. Varying it by scene rather than applying one level throughout tends to serve both requirements.

It also produces a useful texture, since a burst of precise language followed by a stretch of plain description reads as a change of register, and register changes are part of pacing.

Research is cheaper than it looks

Getting terminology right requires a surprisingly small amount of reading, usually a few hours with material written by practitioners rather than by other fiction writers. That is a much better source, since fiction propagates its own errors, which is how a mistake becomes a convention.

Where possible, having somebody who knows the field read a draft catches the remaining problems. Most people are pleased to be asked and the corrections are usually small and specific.

Using specialist language well

Decide the density deliberately, vary it by scene, define through context, use vocabulary to characterise, describe plainly when unsure, and check a draft with somebody who knows. That is all of it, and it applies to any specialised subject rather than only this one.

Characters here are fictional and unmistakably adult, as set out in the reader agreement.