What is 'object_table' and 'object_id' in Acl API?
Object table is the type of data the ACL is operating on. 

For eg: if you want to create an ACL which grants permission for an event - object table, in this case, will be civicrm_event.

Object id is the id of the event to which the permission is applied to. An example of API which uses these two params could be -

$result = civicrm_api3('Acl', 'create', [
  'object_table' =&gt; "civicrm_event",
  'object_id' =&gt; 2, //event id, 0 for all events.
]);