Implementing hook_ENTITY_TYPE_access

Apologies for the elementary question, but what exactly do capital letters mean in a hook?  

I know capital letters indicate special handling in Drupal (similar to a parameter for naming hooks?).  So in custom modules, is it correct to say that ENTITY_TYPE in a hook name should be replaced with a value?

e.g. In the custom module, “mymodule”, would you implement hook_ENTITY_TYPE_access as follows?

<?php 
/* 
function mymodule_{something special goes here}_access($entity, $operation, $account) {
//...
}
*/
function mymodule_node_access($entity, $operation, $account) {
//...
}

What about those hooks with a name containing ” _entity_type_” in lower case? Are these meant to implemented as-is?

Thanks.

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