If you've known what someone was going to say right before they said it, or maybe you said the exact same thing as someone else at the exact same time, that's intuition.
Sometimes we know one another so well that we're able to finish each other's sentences or even communicate with just a look. We might be so in tune with the other person that we just know what they'll say (or what they're thinking). Sometimes this can happen with people that we don't know as well, but not as often. This is when your intuition is working really well! You're clairvoyantly picking up on what they're about to say right before they say it. You're connecting with their energy and with them on a soul level.
Your telepathic ability comes into play when you either think the same words at the same time as someone else, or you verbalize those words and both of you say the same thing at the same time. This tends to happen more with people that you're close with than strangers because you're more in tune with their energy and have a connection with them. Best friends, couples or twins tend to have this type of connection a lot. Sometimes they'll only have to look at each other and instinctively know what the other person is thinking.
I've even seen this happen with songs on the radio, where you're singing the words to a song that you've never heard before. If you'd like to practice your telepathy or heighten your intuition, there are a few different ways that you can do it, like trying to sing songs on the radio that you don't know, finishing people's sentences, or guessing what someone is thinking about in that moment, are easy ways to jump start the process. Be sure to clear your mind, and mention everything that you're seeing, hearing and feeling, no matter how weird you think it is - go for it.