Focus refers to the point at which attention is centred around, our innate ability to tune into a sound or visual and block out surrounding distractions to direct more attention at a specific thing, this natural ability allows us to maintain a 3conversation with background noise or read a single word in a book without becoming overwhelmed. This can also be achieved via simulation or pseudo focus, images or videos can be manually focused by using blur and depth of field to bring the desired object to the centre of attention, as with audio, unnecessary audio can be muffled and lowered to draw attention to the primary source of information.
An image I took of my coffee cup - the cup in focus while everything else blending together in the background.
By listening to all the elements, it's easy to pick out one specific sound and focus on it.
Focusing allows us to process and pick something specific out of a lot of data, this process is used to allow the brain to filter through useless information to get to essential stuff - an interesting mechanic once broken down
Things I learned
Without focus we'd be lost and bombarded with information we couldn't process at once like a computer asked to execute several thousand large processes at once, we'd crash and be unable to pick out coherent data.