* New Words: Language is constantly evolving. New words are coined, existing words take on new meanings, and slang terms become popular. Dictionaries are updated periodically, but they can't keep up with the constant influx of new vocabulary.
* Technical Terms: Dictionaries typically focus on general vocabulary. They may not include specialized terms from specific fields like science, medicine, or technology. These terms are often found in specialized dictionaries or glossaries.
* Regional Dialects and Slang: Dictionaries primarily focus on standard English. They may not include words that are specific to regional dialects or slang, which can vary greatly.
* Proper Nouns: Dictionaries generally don't include proper nouns (names of people, places, or organizations).
* Infrequent or Obscure Words: Dictionaries prioritize common words and may not include very rare or obscure terms.
In summary, an unabridged dictionary is a comprehensive resource for the English language, but it's not a complete list of every single word ever used. It's a snapshot of the language at a particular point in time.