Both climbers are tied to the rope at all times, and both make sure that there are several points of protection in situ between them.
In such a scenario, the concept of a 'pitch' is redundant as the pair keeps moving through the belay stations that mark the end of a normal pitch.
A classic example is the 1,800-metre (5,900 ft) 1938 Heckmair Route (ED2, V−, A0, 60° snow) on the Eiger, which has 7-10 sections that most parties will lead climb as individual pitches (e.g. "The Ice Hose", "The Ice Chimney", "The Quartz Crack"), while much of the rest of the route can be simul-climbed as a continuous pitch.
For example, many speed climbing pairs on the 31-pitch route, The Nose, use simul-climbing on the easier established pitches, thus reducing the number of actual pitches (i.e. a 'leader' being belayed by the 'second' who is static) that they need, which significantly speeds up their rate of ascent.
The techniques of simul-climbing and free solo climbing—both of which avoid climbing in 'pitches', as there is no need for a belay—involve significantly greater risk to the climber(s), but by definition make the concept of a 'pitch' redundant.
[12] The term 'pitch' is also used by cavers to refer to a very steep or vertical section (called a drop, pit, pot, or a shaft) in a cave that needs ladders or single rope technique to descend and ascend (a drop that can be descended and ascended without equipment is a 'climb').