Depending on what day of the week it is you’ll probably see a number of posts on social media featuring the same social media shorthand and there are new ones popping up all the time. You’ve got your classic #TBT and #WCW but now there are variations of these as well.

Whether you’re on Snapchat, Instagram or Facebook you’ve probably gotten used to seeing these shorthand acronyms for different posts but maybe you haven’t know what they all stood for. Even each social media platform has its own acronyms or shorthand for referring to them, for instance Facebook is FB, Instagram is IG or Insta and Snapchat is simply Snap.

Some of the acronyms depends on which day of the week it is. For example on Monday, you might see the vague #MCM. On Thursdays you’ll probably see some posts tagged with #TBT. Here’s what they mean, so next time you see one you’re not left wondering what the significance of the photo is.

The week on social media starts with #MCM.

#MCM - This one stands for “Man Crush Monday.” A photo with this below it means the poster has a “man crush” on whoever the photo is of, whether it be a celebrity, a boyfriend, a dog, or whoever the photo is of. This is strictly used on Monday.

On Wednesdays you’ve got #WCW

#WCW/#WCE - This one stands for “woman crush Wednesday” or “woman crush eternity.” They’re similar to #MCM but they’re posted of women, so a significant other, celebrity or any important female figure to the poster. This post from Jennifer Aniston’s husband Justin Theroux is a good example of one.

Thursdays are reserved for #TBT.

#TBT - This means “throwback Thursday,” and is meant for Thursdays, not Tuesdays. This is usually an old photo from months or years ago. What exactly constitutes a “throwback” is somewhat vague. Actor Mark Ruffalo posted this #TBT of him from his early acting years on Twitter.

For those who missed #TBT, there’s always #FBF.

#FBF - This one stands for “flashback Friday.” It’s basically the same thing as #TBT but it happens on Friday, perfect for anyone who forgot to post on Thursday.

There are other acronyms as well that are less centered on specific days of the week and are just used whenever they fit the situation.

#LB - This means “like back” people comment it on other user’s posts asking for a like back on one of their posts. This got particularly popular a few years ago when people kept commenting “LB” on Kylie Jenner’s photos and she tweeted asking them to stop.

#DM/PM - This means “direct message” or “personal message.” This means someone wants to have a private conversation with another user that others can’t see.

#HMU - This can also be a conversation starter, it means “hit me up,” which basically means message or call me.

#ICYMI - “In case you missed it” this one is used to catch someone up or to bring something important up again.

#BTW - Simply short for “by the way.”

#FOMO - This is the fear of missing out, something we’ve all experienced at one time or another.

#NSFW - This one is important if you’re scrolling through any of your social media in the office, it means “not safe for work” so you probably shouldn’t view it at your desk.

#TBH - Sometimes someone will comment this on another person’s profile if they want them to give them a “tbh” or a “to be honest” comment.