Unconditional love means to love someone regardless of their actions, words or behaviour. You love them no matter what. Usually we love people based on qualities they display or what they give us. We become strongly attached to people for various reasons and we call that love.
I think that saints (very deeply spiritual people who have come close to God) have the ability to see God in everyone. They can practise universal unconditional love. But for the ordinary human being, unconditional love is also possible. This type of unconditional love is not universally applied because we cannot see that deeply. It is a specific, contextualised love which comes from knowing a person through and through. We develop unconditional love for someone whom we feel very closely connected to.
It’s the way a mother feels towards her child. A couple may reach this place of unconditional love over time. This type of genuine, accepting, forgiving, embracing love is totally contrary to the illusionary romantic love we see in films. That kind of love is more about the ego, or what we want to get from another person. Unconditional love is selfless, but still strong and assertive. It reaches out to the other person. It has courage, stability and faith. Even if someone thinks that they are ‘unworthy’ of love for various things they have done, crimes they may have committed, through the eyes of unconditional love, that person has the ability to redeem themselves.