Gyakugatte literally mean opposite sides. In this context it means a temae in which the guests are seated to the left of the host. Normally the guests are seated to the right of the host. This only works with some temae and some dogu. As a general rule you can only do it with symmetric tanas. Maru-Joku would be one such tana.
It is a common misconception that the temae is done opposite in gyakugatte, meaning that you would do everything you normally did with right hand with left and so on. This is not the case.
Before Rikyu it was common to have the guest on the left side. It was Rikyu who changed it to the right side.