Fleeting notes

Fleeting notes are all the ideas that pop into your head throughout the day, that you capture and maybe turn into something more concrete.

Most people capture these kind of ephemeral notes. The specific term 'fleeting notes' is from Zettelkasten I believe, where they're given a bit more purpose.

These are all the ideas that pop into your mind. Always have a notebook or a note taking app with you to capture these. They can be very short—just one word for instance. The goal is just to remember them for a very short amount of time, until you can sit down and write a proper note

– How to take smart notes - Ness Labs

You should have an easy way to capture them. See How I capture fleeting notes.