In PHP, single quotes (' ') and double quotes (" ") are used to define strings, but they behave differently.
Single quotes treat everything inside them as a literal string. Variables within single quotes are not interpreted, they are treated as plain text.
Double quotes allow variable interpolation. When a variable is placed within double quotes, its value is replaced within the string.
In general, single quotes preserve the literal value of each character within the quotes, while double quotes allow for variable interpolation, treating the content within as a mix of literal text and variable values.