Affect is a broad psychological term for feeling-related experience, including how pleasant or unpleasant, energised or subdued a moment feels.
It can be less specific than a named emotion. There may be unease before you know whether you’re anxious, embarrassed or simply tired of the noise.
"Something feels off" is a beginning.
You enter a room and feel yourself become quieter. Nothing obviously bad has happened. You don’t yet have a neat explanation.
You can notice the change without inventing a cause to justify it. Is there tension? Heaviness? A wish to leave? Does anything change when someone you know begins speaking?
The word affect is useful in psychological reading. In your own notes, "heavy and a little restless" may tell you more than the technical word does. Precision isn’t the same thing as sounding academic.
For the difference between a passing response and the atmosphere of a whole afternoon, compare emotion with mood. Both can matter before you’ve found a reason for them.
Noba’s Emotion Experience and Well-Being places emotional experience in the context of everyday life and well-being. It is useful background when the broad term affect feels less familiar than the feelings it describes.