The definition on OALD is identical for parcel and packet.
parcel (especially British English) (North American English usually package) something that is wrapped in paper or put into a thick envelope so that it can be sent by mail, carried easily, or given as a present
packet a small object wrapped in paper or put into a thick envelope so that it can be sent by mail, carried easily or given as a present
According to OALD, package is a North American term, though ngram viewer indicates that it is also the most common word in British English.
What is the difference between packet, parcel and package? Do the words denote size or material (package in its second meaning)?
Best Answer
Mostly conjecture and original research:
A parcel has the modern connotation of being sent by mail, and you normally never hear of the noun used to describe anything else (though you may sometimes hear it in verb form, meaning "to deliver in regular, divided amounts"). The word originated from the Old French parcelle meaning "a small piece or part".
A package also generally has the same connotation. The word evolved from "pack" which has its roots in Old German, to basically mean "the product of packing" similar to the etymology of "baggage". While a package is often sent by mail, you could hear of a "package" being stored, or of a "gift-wrapped package" being delivered in person.
A packet is a newer word, with forms first appearing in the 1500s (vs the 1200-1300s) in Middle French (pacquet). The word originally meant "bundle", but now typically has one of the following connotations: