1.identifying the agent performing an action:
after a passive verb.
“the door was opened by my cousin Annie”
synonyms: through the agency of, by means of, under the aegis of, using, utilizing, employing, with the help of, with the aid of, as a result of, because of, by dint of, by way of, by virtue of, via, through
“he was arrested by the police”
after a noun denoting an action.
“a clear decision by the electorate”
identifying the author of a text, idea, or work of art.
“a book by Ernest Hemingway”

“malaria can be controlled by attacking the parasite”
indicating a term to which an interpretation is to be assigned.
“what is meant by ‘fair’?”
indicating a name according to which a person is known.

“she mostly calls me by my last name”
indicating the means of transport selected for a journey.
“the cost of travelling by bus”
indicating the other parent of someone’s child or children.
“Richard is his son by his third wife”
indicating the sire of a pedigree animal, especially a horse.
“a black filly by Goldfuerst”
(followed by a noun without a determiner) in various phrases indicating how something happens.
“I heard by chance that she has married again”

“the shot missed her by miles”
indicating a quantity or amount.
“billing is by the minute”
in phrases indicating something happening repeatedly or progressively, typically with repetition of a unit of time.
“colours changing minute by minute”
identifying a parameter.
“a breakdown of employment figures by age and occupation”
expressing multiplication, especially in dimensions.
“a map measuring 400 by 600 mm”

“I’ve got to do this report by Monday”
synonyms: no later than, in good time for, at, before
“please be there by midday”

“remains were discovered by the roadside”
synonyms: next to, beside, next door to, alongside, by/at the side of, abreast of, adjacent to, cheek by jowl with, side by side with; More
past and beyond.
“I drove by our house”
synonyms: past, in front of, beyond
“go by the building”