In music, a ritardando indicates a decrease in speed. The number of bars over which this decrease takes place is indicated by an ellipsis, just as with an accelerando . Where the accelerando tends to be steady, measured, and longish, however, the ritardando tends to be shorter and more dramatic, as if it’s slowing down to make a point.
Ritardando is a Directive card, directing the querent to slow things, or themselves, down. It can also indicate things grinding to as if to a halt, or an increasing lethargy: suddenly, one is wading through deep mud. Or there may be a beneficial slowing, an easing into a more manageable pace.