Its when your focus is on what you like about another. We look at them and feel this sweeping appreciation for who they are, their joy, their insights, their humor, their companionship, etc. Love is wanting another to feel good. We want those we love to be happy, safe, healthy, and fulfilled. We don't always express our love.
Love is a feeling and the expression of that feeling is separate.
It's an action. There's a practical reason we don't always express our love for another. We only have 24 hours in a day. If the expression of love was a core ingredient to love, we would have to be stingy with who we loved. If you see the distinction between the feeling and the expression, you can then love endless numbers of people.