This is a piezoresistive force sensor from Tekscan.
The harder you press, the lower the sensor's resistance. Pressing hard, the resistance changes from infinite to ~50k.
The sensor itself is thin and flexible, but the resistance does not change while being flexed.
Resistance changes only when pressure is applied to the round area at the end of the sensor.
Used as a presence sensor (someone standing), weight sensor, pressure sensor (impact testing), etc.

The overall length is about 57mm. The sensor comes with a 2,5mm spaced, reinforced, breadboard friendly connector.

This sensor ranges from 0 to 11 kg of pressure.

 

Documents:

• Datasheet (ZFLEX A401-25)
• Sparkfuns Flexiforce Pressure Sensor Quick Start Guide
• Product Page
• Bildr Tutorial