Love is the warm feeling of affection and care you feel towards someone or something.
There are 4 kinds of love
1, Agape is the highest form of love guided by principle. God and Jesus his son showed this kind of love towards mankind. it is a sacrificial and unconditional love.
2. Philia is friendly love
3. storge is your love for fleshly brother
4. erros is romantic love
5. Platonic is a friendly love between opposite sex, they claim it that way but usually it falls to erros or erotic love
You can say I love you to anyone depending on what kind of love you feel.
I guess I defined them all