What does it mean for something to exist? And what does it even mean for something to be real?

I'm not just talking about concrete objects, I'm talking about anything. Thoughts, feelings, emotions, concepts, the laws of nature, the laws of maths; where do they exist? In what sense do they exist? <br><br>What does it mean for something to be real?<br><br>Or in other words, what does it mean for something to be?