Candid (Adjective)-Relating to or being photography of subject acting naturally or spontaneously without being posed.

https://www.merriam-webster.com/dictionary/candid

Taking a photo and the person is not posing for the photo or simply not ready, this is called a candid photo.

Example: As you can see in the picture bellow, one man is ready for the picture while the other two men in the back  are not ready for the picture.