Is it Every Day or Everyday?

Both of these expressions exist in British English. They do, however, have different meanings and are commonly mixed up, even by large British supermarket chains on their in-store signs!

Every day

This is used to mean that something is happening daily, as in the following examples:

* We do this every day.
* Every day, we like to contact Future Perfect.
* Available all day every day.

Everyday

This is an adjective (or describing word) meaning ‘ordinary/regular’, as in the following examples:

* This is an everyday occurrence.
* It’s just an everyday event.
* It’s an everyday object.

The bottom line:

Everyday is a single word and is an adjective, so it's the one that is used in front of a noun to describe something as normal or commonplace.
Every day is an adjective (every) plus a noun (day), and it means each day.