As said in the title, it's a $4$-letter word. I actually found this in my old notebook which I kept like two years ago. Most likely I made this once for my friends to decipher, though I don't clearly think they ever got that and we just most likely forgot about it. So, just wanted to see, if anybody can give it a shot and get it.
To decipher this, you should just get two different concepts behind this which make 50-50 of the decryption. As you can see in figure those two contrasting parts are sure different, one must get the "triangle" part and then move on, instead of just pondering over one thing.
No complicated math-related or pop-culture reference is involved in the process, mostly picture/shape-based. Also it is number-alphabet relation based