wp config – Where should I write the constants in wordpress?

I have to define a constant to use in the whole project (that is: single.php, category.php, my-template.php). Suppose I define an array constant to declare a browser name list. that is: array (& # 39; firefox & # 39; => & # 39; Mozilla Firefox & # 39 ;, & # 39; google_chrome & # 39; => & # 39; Google Chrome & # 39;). Now this constant will be accessible within any php file in my project. I can do this in several ways. But what is the best practice?