Updated comment based on change in method's functionality

Signed-off-by: expani <[email protected]>

server/src/main/java/org/opensearch/search/aggregations/bucket/terms/MultiTermsAggregator.java

@@ -275,8 +275,8 @@ private void collectZeroDocEntriesIfNeeded(long owningBucketOrd) throws IOExcept
     @FunctionalInterface
     interface MultiTermsValuesSourceCollector {
         /**
-         * Collect a list values of multi_terms on each doc.
-         * Each terms could have multi_values, so the result is the cartesian product of each term's values.
+         * Generates the cartesian product of all fields used in aggregation and
+         * collects them in buckets using the composite key of their field values.
          */
         void apply(int doc, long owningBucketOrd) throws IOException;