Macarons are French cookies made with almond and egg whites that are sandwiched around a cream-based filling.  They come in a rainbow of colours and flavours. 

Macaroon is the American word for our version of a flourless egg-white-based cookie.  Most often made with coconut, it can also include nuts or nut paste.  Macaroons are often served for dessert at Passover celebrations, since they don't contain flour.

The sandwich-cookie-style macaron is most often found in Paris.  Another French cookie, resembling Italian amaraetti (also a flourless egg white and nut cookie), is also called a macaron.