Slavisa Jokanovic's side were as low as 17th in mid-November but went on to win 11 of their following 15 fixtures to move up to fifth in the Championship table and are currently just six points off the automatic promotion places.
The Cottagers are also unbeaten in their last 10 league games but now face a tricky run of fixtures against promotion rivals including Bristol City, Wolverhampton Wanderers, Derby County and Sheffield United in the coming weeks.
"It's huge, I think it defines the season," Cairney, who was linked with a switch to West Ham United in January, told Sky Sports News. "All those teams are above us or around us so it's massive. It's going to define what we're going to do this season.
"It's important that we haven't got many in the physio room at the moment so I think we're going to have a strong squad and we're going to need it over the next couple of weeks.
"It's a special run and we've really climbed the table. We're in form at a great time, it's just about maintaining it to the end of the season and we shouldn't be far off."
Fulham travel to Bristol tonight before welcoming Wolves to Craven Cottage on Saturday evening.