Final answer:
Colloquialisms are informal words used in everyday speech that might not be understood outside of a specific community or region, such as the Californian expression 'hella'. They add color to conversation but are often too casual for formal settings.
Step-by-step explanation:
Common words that are not typically included in formal speech but may be used in informal conversations, such as slang, are called colloquialisms. These words are part of everyday speech and are often specific to particular regions or social groups. For example, Californians might use the term "hella" to mean very or a lot, but this colloquialism might not be understood outside of that community.
Colloquial language, including slang and regional dialects, can add color and authenticity to dialogue, but it's generally considered too casual for academic or professional settings. Using colloquial language effectively requires understanding the audience and context to ensure clear communication.