The 30 words you need before you can read the field

You want to start learning something but every explanation assumes vocabulary you don't have yet. This gives the thirty most important terms in the field, each a one-line definition with a practical example, sorted so the words that unlock the others come first. The glossary you read before everything else.

Give me the 30 most important terms a beginner needs to know in [field]. For each, one line of definition plus one practical example. Sort by which terms unlock the others.