A term is considered descriptive if it directly describes a characteristic of the goods or services it is used with, such as the quality, ingredients, intended purpose, geographic origin, or intended users.
"Fizzy and Bubbly" for a soft drink, "Fresh Baked" for a bakery, or "Fast Delivery" for a courier service are all descriptive because they tell the consumer something directly about the product rather than identifying its source. These terms are routinely refused because competitors in the same industry need to be able to use them freely.
A term is not considered descriptive if it requires imagination or inference to connect it to the goods or services. "Jaguar" for cars is suggestive (it implies speed and power) rather than descriptive, which is why it is registrable.