“Do not indulge in dreams of having what you have not, but reckon up the chief of the blessings you do possess, and then thankfully remember how you would crave for them if they were not yours.” -  Marcus Aurelius (121 - 180 AD)

Craving is to want something so much that we take actions consciously or unconsciously that harm ourself, others and/or the environment to get what we want. These actions can be expressed as thoughts, speech, or physical engagements. Some examples may be thinking badly of ourselves for not being good enough; harming or stealing from others to get some basic life needs like food, water, shelter; lying to gain social acceptance; cheating to get greater comfort or money; or killing or controlling people to get more power. 

Craving versus Desire

“From craving is born grief, from craving is born fear. For one freed from craving there’s no grief - so how fear?” -  Siddhārtha Gautama (563 - 480 BC)

Craving and desire can be defined separately to help understand the difference between wanting something and wanting something with an expected outcome. Craving is to want something and to be unhappy if we do not get it, where as desire is to want something, but to be ok if we do not get it. We can desire something, but it is the attachment to the outcome that causes the suffering.