Accelerometer as the name implies measures proper acceleration aka g-force. Triple axis accelerometer measures the vector components of the g-force which means it can detect tilts. Gyroscope on the other hand detects orientation. Unlike accelerometer gyroscopes are not affected by gravity.
When paired together 3 axis accelerometer and triple axis gyroscope can be used in variety of applications such as multicopters, RC planes, video game controllers, etc. Even smartphones ship with these sensors to detect orientation or to be used by apps.This breakout board packs MPU6050 3 axis accelerometer with GY-521 3 axis gyro.