S3ListObjectsResponse.commonPrefixes

Keys that share the same prefix, grouped together (up to 1,000). When counting the total number of returns by this API operation, each group counts as one item.

A response can contain CommonPrefixes only if you specify a delimiter.

CommonPrefixes contains all (if there are any) keys between Prefix and the next occurrence of the string specified by a delimiter. These keys act like subdirectories in the directory specified by Prefix.

For example, if the prefix is notes/ and the delimiter is a slash (/) as in notes/summer/july, the common prefix is notes/summer/. All of the keys that roll up into a common prefix count as a single return when calculating the number of returns.