Lives that experience emotions are deemed sentient beings; killing them constitutes the sin of taking lives because they can feel pain. Plants are not sentient beings as they don’t have emotions; plant-based eating does not result in the karma of taking lives because the plants don’t feel any pain. Unlike the definition of living beings given by people in general, plants are not beings according to the Buddhist definition. There is a difference in how such terminology is defined.
Khenpo's blog published on 29 June 2015