in php, what the heck is ” _e ” ???

I’m trying to delve into php further and figure things out, but I keep seeing what looks like a function getting called: _e. I can’t seem to find where this is defined in the files or if it’s a global defined by php itself – either way, I don’t know what the heck it is.

I’m sure this is an incredibly basic thing and may well already be answered, but I haven’t found it by searching yet and I’m completely lost at this point.

Thanks