Custom commands in Vim are defined via the command command. As I learn new things throughout the week, I like to write them down in a TIL.md file. I found myself constantly running :tabe ~/Documents/TIL.md to open my file in a new tab. To streamline the process, I added the following to my .vimrc:

command TIL tabe~/Document/TIL.md

Now, whenever I want to write down something I’ve learned I can just run :TIL.

User-defined commands must start with a uppercase letter.

More details in :help command, or check out the online vim docs.