There are several reasons for the rejection of a trademark, however, the most common grounds are as follows:
Generic Terms: Words that are commonly used cannot be registered as a trademark. Such as 'sweets', 'sugar', 'milk' are generic words. A company cannot hold rights to such words exclusively.
Descriptive/Detailed Terms: Words or adjectives used to describe a product cannot be trademarked. Words like 'amazing', 'great' cannot be used and will most likely be rejected by the registrar.
Deceptive Trademarks: If a word of symbol misleads the consumer it cannot be trademarked. For example, a proprietor cannot name his beverage 'Alphonso' since it resonates with the Alphonso mangoes.
Offensive Terms: Offensive words or terms that are contrary to public order or morality cannot be registered. Words and symbols that are considered to be offensive or violate commonly-accepted norms of morality cannot be registered as trademarks.
Similar or an Existing Trademark: A trademark may be rejected if it is similar to an existing registered trademark. It would cause confusion amongst the consumers.
Official Marks: Any mark or symbol that may contain flags, official names or hallmarks, state emblems of an international organization cannot be trademarked.