If you don't provide an orderby the parameter in your AEM Query Builder query, the search results will be sorted by the default ordering, which is usually by the node's jcr:score or _score property, depending on the version of AEM you're using and the indexing configuration.
However, the default sorting order is not always guaranteed and may depend on various factors, such as the search query complexity, the indexing configuration, and the version of AEM you're using. Therefore, it's a good practice to explicitly specify the sorting order in your query using the orderby parameter, to ensure consistent and predictable search results.
The default sorting order for fulltext search in AEM Query Builder is by relevance, as determined by the score
The "jcr:score" property is a built-in property of the Java Content Repository (JCR) specification, which is the underlying technology used by CRX. This property is automatically calculated by CRX during fulltext searches and is used to determine the relevance of the search results.