Constants in PHP are similar to variables as they are used to store a value.
Constants differ from variables in some majors ways.
1. Instead of a $ and assignment = operator format, constants use a define() function where the formatting is standardized by having the name first listed within the function, plus it must be capitalized (meaning it is case-sensitive) and it must start with a letter or underscore.
2. The value of constants cannot be changed once defined.
3. Constant names cannot be put within quotation marks as seen by the echo statements and string concatentation used above.
4. Constants can be accessed from anywhere in the script, making them global unlike variables, and better for configuring foundational information like files and settings to stay the same.