Why is a glossary essential in requirements engineering?

It pins down a shared vocabulary so people don't silently interpret the same term differently — catching synonyms, homonyms, jargon, and "everyday" words with special meaning.

Terms that need definition:

• Context-specific technical terms: Domain jargon that outsiders don't know
• Abbreviations and acronyms: What does "SRS" mean in your context?
• Everyday concepts with special meaning: "Customer" might mean different things
• Synonyms: Different terms with the same meaning (order/purchase)
• Homonyms: Identical terms with different meanings ("client" = customer or software?)

A glossary:

• Creates shared vocabulary
• Prevents misunderstandings
• Should be created early and maintained throughout
• Is part of the requirements document