You don't even have to say complete sentences to understand what the other is saying. If someone else was looking over your shoulder at your text conversations, it's obvious you're speaking in code. Though, to you both, those one word responses can speak a thousand words.

When you post a cute throwback pic on the 'Gram of you two together, to everyone else, it probably looks like an adorable photo from high school. Though, you both know the history and story behind that specific photo. From one pic, you're transported to a different time, and you know exactly who you had a crush on then, and whether you bought that shirt at Delia's or Limited Too. One pic can seriously make you laugh hysterically, and no one else would think it's funny.

You are your friend's go-to person for any pep talk. You know exactly what to say when trying to cheer your friend up after a breakup, or build up her confidence for a job interview. Unlike anyone else, you're able to pull some examples of past experiences when she got over someone else and totally rocked it at a job to show your friend how awesome she really is.

You and your bestie quote lines from your favorite movies and TV shows you watch together all the time. It's kind of your thing, even if other people just don't get it. In fact, while you're watching movies, you both laugh at the same quotes or parts automatically.

Facebook allows us to keep in touch with people from our past, like high school, who we haven't talk to in years. When someone pops up on your feed, your bestie is able to remind you of how you know that person and also jog your memory with a fun story from school that you may have forgotten all about.

You've spent so much time at your best friend's house that it's like you live there as well. That means you know her family like they are your own. They may have quirks like all families do, but you accept them as your own and joke about family baggage together, because you both get it.

You spend so much time together that you've definitely celebrated some holidays over the years with each other. You may even have some holiday traditions together like spending Christmas Eve at her house. You'll never forget that one Christmas where you got to see your bestie's aunt sing "Jingle Bell Rock" after having too much spiked eggnog. It truly is a story you had to be there to understand.

Every best friendship comes with a few solid nicknames. You may even have a million nicknames together, but every single one of them has a special backstory. You might not even remember exactly how each name started, but know they totally made sense at the time.

Sure, you have your anniversaries to celebrate, like when you met each other or the very day you became best friends. Maybe it's your graduation from high school, or even the day you moved to the neighborhood. Some are just celebrations that come from inside jokes. I text my BFF every April on the day he broke his arm, because it's my "I'm glad you're OK and in my life" holiday that we share together. You won't find a Hallmark card for these anniversaries, but that's what makes them so personal.

Your best friend could write a novel of all the embarrassing secrets you've shared with her, and thank goodness you trust her with your life. She would never tell a soul, but she will, from time to time, drop one word hints of those embarrassing secrets to make you both laugh. Like, saying the name of your middle school crush to make you cringe a little.