Adobe Premiere Rate Stretch Tool
The rate stretch tool is used to change the duration of a clip in the timeline while simultaneously adjusting the speed to compensate.
In the example below, the first timeline shows three clips with a gap between clips 2 and 3. Let's assume that clip 2 has no more available footage but needs to fill the entire space between clips 1 and 3. Using the rate stretch tool you can stretch the clip until it fills the gap.
Importantly, the speed of the clip must be slowed down in order for this to work. Notice how clip 2's title now says Clip 2 [75%], indicating that the speed has been slowed to 75%.
If a clip is reduced in length using the rate stretch tool, it's speed will be increased.
Obviously rate-stretching is not always a good option. Sometimes it is not an acceptable solution, sometimes it is a compromise you can live with, sometimes it is the exact effect you need.