As others have mentioned it's the main group of riders in a bike race. However, as is the case in this context, it can also be used to refer to the race in gene

As others have mentioned it's the main group of riders in a bike race. However, as is the case in this context, it can also be used to refer to the race in general, given that in the TdF all the riders will generally finish each stage within an hour or so of each other (or else be disqualified) and start the next one all together.