Your written instructions that tell the computer what to do. These instructions need a lot of translating for your computer to actually know what you’re typing about, but you don’t have to worry about that.
Like telling a translator how to make a cup of tea, and then them relaying those instructions to someone else in another language. You writing the source code is the instructions to the translator, and the these terms are then translated into something your computer can understand.
Basically, source code + translator = program.