Best Constant to use to check if WordPress is running

I don’t know if others CMS or system may use ABSPATH or not but it’s seems to be a generic words.
I think I would check for a only-WP constant as WPINC or check if a WordPress function or Class exists

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)