Not every mark can be registered as a trademark. The reason for this stems from the very purpose behind trademarks. The goal of a trademark is to signal a single source of goods and services to the consumer and protect the intellectual property of a brand that did a good job of being recognizably unique in its line of business. Registering any mark may fail to meet one or both of these requirements. Some marks are merely descriptive of the goods and services they sell, while others may be too similar to already registered trademarks, which can potentially create consumer confusion and infringe on the existing trademark's rights.
Therefore, the corresponding intellectual property office will assess the trademark application against two criteria: distinctiveness (the ability to be distinguishable) and lack of similarity-based conflict (not conflicting with any similar registered trademark - either because no similarities exist or are resolved during the process).