Most frequently it has been related to the future course of policy rates, but the ECB also provides forward guidance in relation to its asset purchases.
In fact, ECB’s forward 2/9  BIS central bankers' speeches  guidance currently links the lift-off date for interest rates to the end of net asset purchases by stating that “we expect the key ECB interest rates to remain at their present levels […] well past the horizon of our net asset purchases.” The effectiveness of forward guidance is however, a hotly debated topic, both in academia and in policy circles.