what does 'being sentient' mean?

In Buddhism, sentient beings are beings with consciousness, sentience, or in some contexts life itself. Sentient beings are composed of the five aggregates, or skandhas: matter, sensation, perception, mental formations and consciousness. In other words, a sentient being is one with the faculty of sensation and the power to perceive, reason and think. We use this terminology to describe the human experience—and when we design, we are striving to improve that experience by affecting one of the five skandhas.