what is an associative array?

What is an associative array? I am getting an error when I try assign the following to Item before sending this to the server. The error is "\n[Item] must be an associative array. Found <pre class='xdebug-var-dump' dir='ltr'>\n<small>C:\fullpath to my vendor\aws\src\functions.php:252:</small><small>string</small> <font color = ..."

$params = [
   'TableName' => $tableName,
   'email'=>$admin_email,  //sort
   'year'=> $year,        //partition
   'Item' => $encoded_data

The $encoded_data variable is 

$encoded_data={"survey_compiler":"[email protected]","campaign":"Apple","compiler_relation":"private","admin_email":"[email protected]","year":"2010","employee":"Bandfrom Bossanova","employee_email":"[email protected]","employee_id":"","task1":"adapting to a customers needs","task1_percent":"1","task2":"","task2_percent":"0","task3":"","task3_percent":"0","task4":"","task4_percent":"0","task5":"","task5_percent":"0","task6":"","task6_percent":"0"}


I think that Item is an associative array. What a strange error message.

proof that an old dog can learn new tricks