WordPress at a glance
action is not described

woocommerce_account_(key)_endpoint action-hook . WC 1.0

Usage

add_action( 'woocommerce_account_(key)_endpoint', 'action_function_name_8786' );
function action_function_name_8786( $value ){
	// action...
}
$value
-

Where the hook is called

woocommerce_account_content()
woocommerce_account_(key)_endpoint
WC_Shortcode_My_Account::output()
woocommerce_account_(key)_endpoint
woocommerce/includes/wc-template-functions.php 3082
do_action( 'woocommerce_account_' . $key . '_endpoint', $value );
woocommerce/includes/shortcodes/class-wc-shortcode-my-account.php 91
do_action( 'woocommerce_account_' . $key . '_endpoint', $value );

Where in WP core the hook is used WooCommerce

woocommerce/includes/wc-template-hooks.php 291
add_action( 'woocommerce_account_orders_endpoint', 'woocommerce_account_orders' );
woocommerce/includes/wc-template-hooks.php 292
add_action( 'woocommerce_account_view-order_endpoint', 'woocommerce_account_view_order' );
woocommerce/includes/wc-template-hooks.php 293
add_action( 'woocommerce_account_downloads_endpoint', 'woocommerce_account_downloads' );
woocommerce/includes/wc-template-hooks.php 294
add_action( 'woocommerce_account_edit-address_endpoint', 'woocommerce_account_edit_address' );
woocommerce/includes/wc-template-hooks.php 295
add_action( 'woocommerce_account_payment-methods_endpoint', 'woocommerce_account_payment_methods' );
woocommerce/includes/wc-template-hooks.php 296
add_action( 'woocommerce_account_add-payment-method_endpoint', 'woocommerce_account_add_payment_method' );
woocommerce/includes/wc-template-hooks.php 297
add_action( 'woocommerce_account_edit-account_endpoint', 'woocommerce_account_edit_account' );