In computers, an executable is a file the machine can run as a program — not a picture you look at or a text you read, but something that starts doing work when you open it. On Windows people often notice .exe on the end. As an adjective, executable means “able to be run”: executable code, an executable file. IT people and anyone installing software use it. Though actually, outside computers the same shape could mean “able to be carried out” (an executable plan), but that use is rarer; the file is the meaning you will meet. A photo, a song, or a Word document is not an executable, even though you “open” those too.